Brett H. - 89GTA

My GTA has been stalling at idle (Park or Drive) but runs great otherwise. Barely resting my foot on the gas keeps the car running OK. With my scanner I can see the ECM running the IAC up and down somewhat to try to keep it from stalling. The ECM runs the IAC down to 0 and then it stalls. I figured I had a vacuum leak on my hands, so I replaced the EGR valve and the EGR temp sensor since the wire on it broke when I took it off the old EGR valve. I have also replaced the intake manifold gaskets and the plenum/runner gaskets. No help. I unplugged the vacuum from the EGR valve to make sure the EGR solenoid wasn't just stuck...no help. The TPS is rock solid at idle, right around 0.54V. The IAC is apparently working since the ECM can control the idle speed, but for some reason the ECM is running it down to 0 and stalling the engine. I have cleaned the IAC valve pintle and throttle body passages. The engine stalls in both open & closed loop. I took a vacuum reading on it @ 900 rpm and it was steady at about 17". The fuel pressure is OK, but it is bouncing around a bit more than I remember. However, the car drives fine out on the road so the fuel pump is probably OK. The O2 sensor, spark plug wires, and distributor cap were all replaced about 2 months ago (long before the problem started). The power brake booster holds vacuum OK.

Sometimes the engine will idle fine for a short while, but then starts stalling again. Everything that could affect the idle seems to be working, but the car still stalls! I'm out of ideas...can anyone offer any advice?

dnovotny

I had this type of problem a long time ago. Discovered that the spark plugs used for my tune-up weren't ACDelcos (not sure what brand). Replaced them with ACDelcos, problem gone. I looked at the pulled-out plugs, and there was nothing unusual on them.

This was all before I started doing my tune-ups. Now, I have the sratches on my arms to show for it, but I always use ACDelco, never had a problem since.

Dave '91 GTA, '91 T/A

8Mike9

While you have the scanner plugged in, take a look at the CTS readings and the IAC at the same time.

Did you actually take the TB apart and clean it, or just spray cleaner through the passages?

Brett H. - 89GTA

Spark plugs are AC Delco; wires, cap, and rotor are MSD.

The CTS reading agrees with the reading on the dashboard temp gauge. When I cleaned up the throttle body I pulled it off; I did it at the same time I changed the intake manifold gaskets. It's been cleaned twice in the last year so it's pretty close to spotless. When I cleaned it I pulled the IAC out of it, but left the TPS on. However, I made triple sure that I didn't get any throttle body cleaner in the TPS. It worked for a year after the first cleaning before this problem showed up.

formula90

Just because the CTS reads the same as the dsahboard temp does not mean its good. You have to check the cts with a multimeter...


"Here are some of the problems associated with a faulty CTS:

Hard starting, or no start
Surging
Incorrect idle (too high or too low)
Incorrect shift points and/or no converter lockup
Poor gas mileage
Backfiring
Incorrect idle mixture (cold or hot)
ECM won't enter closed loop operation
Spark plug fouling
Catalytic converter damage
Hesitation and/or stalling
Overheating


Check the CTS resistance directly with a digital voltmeter. Compare the resistance readings with the accompanying chart. Remember the values do not have to be exact, just reasonably close.
If the resistance is out of whack, replace the CTS. If the resistance values are on the money, check the connection of the ECM harness. If the connector is OK, the ECM is faulty and should be replaced.

Remember that a faulty CTS will not always cause the ECM to activate the check engine light. If the vehicle is experiencing any of the symptoms mentioned above, it is worthwhile to check the CTS resistance first, since it is so easy to do. You will need to have a decent idea of what the actual engine temperature is; a "probe" type cooking thermometer works very well for this purpose, but any type of thermometer that can stand the heat will do. Once you have a good idea of the engine temp, disconnect the CTS harness and connect a digital voltmeter across the CTS terminals. Use the chart below to compare your findings:"

Temperature (F) CTS Resistance (ohms)
210 -----------------------------185
160 ----------------------------450
100 -----------------------------1800
70 ----------------------------3400
40 --------------------------7500
20 -------------------------13,500
0 -------------------------25,000






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Brett H. - 89GTA

I'll check the CTS with a multimeter. I figured it was OK since it was also reading 200 degrees when my fans kicked on, which is the temp that my fan switch turns on. Checking it is easy enough. The car seemed to behave much better this morning in open loop, but still stalled when warmed up.

I'm also going to check to make sure that something isn't shutting off power to the fuel pump at idle (not too likely, but possible). I'm also going to take a look at the MAF since the ECM thinks the engine is taking in more air than it really is.

El Guapo

Off the wall idea, but here is what I see.

Sensors are ok, the car just chokes itself to death.

Have you set the idle set screw? It is usually on the left side of the throttle body. It will have a cap on it. By setting this, you will not allow the airflow to drop down low enough to cause the car to stall.

Here is what you do.

1) Get the IAC valve set to zero
2) If the car was running, turn it off
3) Disconnect the IAC
4) Locate the adjustment screw (remember, it may have a cap over it.)
5) If there is a cap, use a hammer and nail to punch through the cap and remove it.
6) Turn the screw a 1/2 turn clockwise
7) Try to crank the car
8) If it wont crank, repeat steps 6 and 7
9) Once running, turn the screw counterclockwise till the RPMs are about 450.
10)Turn off car
11) Reconnect the IAC
12) Take it for a test drive


The reason you set the RPMs w/o the IAC at about 450 is because that is a BACKUP. your RPMs dont need to normally be that low, but if your IAC acts dumb, you should be ok.

Any questions email me

Clayton

Brett H. - 89GTA

Yeah, I had considered resetting the minimum air. The engine seems like it gets down to about 700 rpm and just quits, like right now. I'm not even sure if it would stay running at 450 rpm. This was going to be my last resort since I didn't want the IAC to stay closed all the time. The car ran absolutely perfect before last Friday, it just started this crap all of a sudden. It sure acts like a component failure of some kind. I'm willing to try about anything though...

RoadRocket L98

Could someone tell me what the CTS is? My car has a lot of those symptoms that formula90 mentioned. I've no idea what it is or where it is or how much to replace? Anyone wanna enlighten me?

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'89 Firebird Formula 350
L98, WS6, Red/grey, t-tops, and a 3.27:1 rear
K&N, TB bypass, no MAF screens, CAI, full Accel ignition, no cats, Hooker Supercomp shorties, Hooker 3-inch catback
ET? The POS runs 15s.
Also own '83 Firebird 2.8 2bbl. 155K miles.
ET? Break out the calendar!

Brett H. - 89GTA

The CTS is the coolant temperature sensor. It is located on the front on your intake manifold. I haven't had to replace mine (yet) so I'm not certain how much they cost.

Vader

Brett,

Are the injector pulses running at about 3mS (approximate time)? Did you lightly lube the IAC pintle when you cleaned the control? Did you try bypassing the EST circuit to eliminate that variable at idle?

Just some random thoughts...

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Later,
Vader
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"Fear is how I fall, Confusing what is real..."
Adobe Acrobat Reader

formula90

the CTS is maybe 6 bucks at any parts house. it would be a no brainer to replace, plus it just makes sense for piece of mind, it definitly will not make your problem worse. The CTS is involved in a majority of the engine management controls by the ECM and is worth every penny replaceing since you are troubleshooting a problem anyhow.

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Brett H. - 89GTA

Injector pulses are running about 1.5ms until the ECM (or me) tries to save the engine from stalling, at which time the injector pulses run up to about 3ms. I didn't lube the pintle on the IAC valve. I can try that too; maybe it just can't run fast enough to accurately follow the ECM's commands. I'll try that. I did an experiment last night to see if I'd even be able to set minimum air, and the engine shuts down at 700 rpm. It will not run below that. Above that it runs absolutely perfect and you'd never know anything's wrong. I'm going to check the PCV and CTS today, and I'll bypass the EST too. Maybe it's time to stop the troubleshooting and just throw a few parts at it.

El Guapo

You didnt say you have pulled the Spark Plugs recently. By not being able to go below 700 RPM, it sounds like maybe youre not hitting on all cylinders, at least not at idle. If they are worn, the gap will have increased which will result in a weak spark, which could get to the point of not firing at all. Or, it could be fouled, which would both cause the following.
That would cause the engine to have to turn higher than normal RPMs to make enough energy to turn the V8. They would also cause unburt gas to get to the O2 sensor which would make the sensor think the engine is running rich which would make it try to increase airflow AND reduce fuel, till it wouldnt fire right. At that point it would try to dump fuel back in, but too late, flame out.

The above sounds logical. What would cause it though?

Im thinking:
Spark Plugs
Possibly damaged SP Wires
CTS

All of these are things related to the spark and things that could have gone Kaput! recently.

My first action after it dies, would be to pull the plugs. You would recognize the fouled one(s). Then I would replace all the plugs and see if that helps. If not, then I'd take a hard look at the wires.

If it still did it, then l'd throw a CTS at it.

Just me though

Good luck
Clayton

El Guapo

Then there is the other side of the equation. What if you had a clogged injector? You would be able to tell that by fining a plug that was white instead of the normal tan.

Im thinking not, but it could be.

Just another thought from yours truly
Clayton

soulbounder

My car was doing pretty much the same thing and I had the hardest time figuring out what it was. Everything pointed to the CTS, so I pulled off the connector, and I didn't need a multimeter to tell me it was bad. It was all rusted and corroded. I don't even know how to check it with a multimeter, lol. But I changed it and never had trouble with it since.

Brett H. - 89GTA

OK, this is interesting.

The PCV and CTS both checked out OK. I monitored the fuel pump sense line when the engine stalls, and the fuel pump is not getting shut off by anything. When I bypassed the EST...it idles fine. Idles at 650 rpm in Drive as nicely as you please. Things I noticed using the scanner with the EST bypassed: 1. The injector pulse has fattened up to 2.5ms, compared to 1.5ms without the EST bypassed. 2. The AIR divert solenoid is turned off. The fact that the engine has now proved capable of running at 650 rpm makes me think it's not a mechanical problem. I hear what you're saying about plugs & wires (and I'll pull some in the morning to be sure) but the plugs & wires are barely two months old, and the car runs GREAT at any speed...except idle. It really acts like the ECM is making the car run very lean. Maybe it's my imagination...but the engine seems to be hotter than I remember when I'm working on it. Stuff under the hood's almost too hot to touch. I'm wondering if that new O2 sensor got contaminated or something. If that's not it, could it be something in the EST system?

El Guapo

Wonder if your timing might have gotten bumped somehow?

The timing being off could cause the hotter than normal feelings AND could cause the problems w/ the EST you mentioned.

The computer obviously move the timing a certain + the base. If the base were off, the amount the computer advances (I think it is) would throw the timing question way out of whach.

Just another quality thought from your friendly SC neighbor.

Clayton

Brett H. - 89GTA

I set the intial timing when I replaced the intake manifold gaskets since I had to pull the distributor. That was last weekend. The problem occurred both before and after the gasket installation. It's times like this I wish I had a couple of idle mixture screws I could tweak...

So, could the EST cause something like this? Or did I just cause the ECM to fatten up the injector pulse by disconnecting the EST?

oldblueZ

Hi guys, I have been having the same problem that just started from out of nowhere. I have not been able to have time to try anything, but could somebody tell me what and where the EST is.

I'm planning on checking(after I find it) the CTS and my spark plugs. Because I was moving the day my car did not want to idle, I just bumped up the idle to where it would idle and not die, 1000 RPM(too high). Now that I have settled in I will have time to check stuff and play with it.

Thanks,
Jesse

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85 Z28, 305 TPI A4
pretty stock with a few toys
15.2@91mph
http://photos.yahoo.com/j_hougnon

http://screamindeamin.cz28.com/images/jesse/

Brett H. - 89GTA

The EST is the Electronic Spark Timing circuit. This is the circuit the ECM uses to control ignition advance. The ECM and the distributor module make up the heart of the system. There is also the ESC (Electronic Spark Control), which is a seperate module mounted on the firewall that works with your knock sensor to tell the ECM that detonation is occurring.

When you set your initial timing by twisting the distributor, you should bypass the EST circuit so the ECM doesn't try to alter the timing while you're adjusting it. This is done by unplugging a tan/black wire in the back of the engine compartment on the passenger side. My stalling problem disappeared when I unplugged this connector, but I'm not sure it is necessarily something wrong with the EST that is the root cause. At least I've eliminated several possibilities by now. I think I'm going to try a new O2 sensor first and then maybe a new distributor module.

Question: If I set the initial timing to 8 degrees with the EST bypassed, what should the timing be when I check it with the EST enabled? Mine jumped up a bunch when the EST was hooked up again. Maybe the timing is overadvancing if something is wrong with the EST?

[This message has been edited by Brett H. - 89GTA (edited May 26, 2001).]

[This message has been edited by Brett H. - 89GTA (edited May 26, 2001).]

Corry

Hey, while we are talking about timing let me get one thing straight. Everyone says to disconnect the EST. Well, I have my helm "official" shop manual (www.helm.com) sitting right in front of me. This is for the 87's. On page 6D4-5 there is a section entitled set ignition timing
it reads word for word-
1. Refer to the tune-up label located in the engine compartment. Follow all instructions on the label.

2. With ignition off, connect the pickup lead of timing light to the number one park plug. Use a jumper lead between the wire and plug or an inductive type pickup. DO NOT pierce the wire, or attempt to insert a wirebetween the boot and the wire. Connect the timing light power leads according to manufacturer instructions.

3. Start the engine and aim the timing light at the timing mark. The line on the balancer or pully will line up at the timing mark. If a change is necessary, loosen the distributer hold down clamp bolt at the base of the distributer. While observing the mark with the timing light, slightly rotate the distributer until the line indicates the correct timing. Tighten the hold down bolt and re-check the timing.

Now I do not see the tuneup label in my engine compartment, so maybe the est wire disconnect would be on there? Otherwise where is everyone getting this from? I just recently set my timing w/ the wire plugged in (was having major lack of power before) and now I have much more power! Should I go back disconnect the EST and set timing again? Thanks!


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Corry Lazarowitz
clazarow@voicenet.com
clazarowitz@hotmail.com
1987 Pontiac Trans AM (GTA?) 350 or is it a 305?! TPI
SLP 1 3/4" headers, 3" cat back (stock cat
MSD ignition.
MSD Blaster SS coil.
3.73 Rear end gears
Accell 8.8 Wires
Bosh +4 Spark Plugs (Don't know if they really help but hell!)
Holley AFPR
Race Built Automatic trans ('vette servo, shift kit, tightly packed clutches)--just needs titanium gears now!
Newly gutted cat (the car gutted it's own cat!)
Hypertech Chip (Just found out I had it! :eek
More soon when funds are avail...

formula90

in 87 you still have the electronic feedback carb. with TBI it is mandatory to unplug the EST connection because if it is still connected while timing the motor, the ECM will just readjust it. That helms manual is just for that year of car, not for every model.

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Brett H. - 89GTA

1. Replaced O2 sensor...no change.
2. Replaced distributor module since it's in the EST circuit...no change.
3. Disconnected AIR diverter and switch connections to simulate what it did when I had the EST disconnected...no change.
4. Disconnected the EST and advanced the initial timing to simulate what happens with the EST hooked up, reasoning that if the timing were advanced more than it should be that it would cause an increase in idle speed, maybe more than the ECM could compensate for. The car still idled OK with it disconnected.
5. Retarded the hell out of the timing, and then hooked up the EST. Engine still stalls.

So what else is there? The only other thing I noticed with the EST disconnected was that the injector pulse was wider, richening it up some. Maybe I ought to try moving the TPS a bit just in case it's sitting on an intermittant spot that the scanner isn't seeing. I'm also thinking about replacing the CTS sensor as insurance. Soon I'm going to pay to make this someone's else's problem (even though I dislike other people working on my car).

Brett H. - 89GTA

Since it drives me nuts when people don't post follow-up to their problem, here goes...

It was the distributor pickup coil. I had checked the pickup coil with a meter before, and it was right at the lower end of the acceptable resistance spec. However, the wires coming up through the distributor had very small cracks in their insulation. Now, how can a pickup coil cause a problem only at idle and not affect the engine at any other rpm is a mystery to me. When I've seen them go bad before, the engine won't even run from the coil being open or whatever. Live and learn...

formula90

thanks brett for posting that follow-up....wow, it was the pick-up huh? makes me wonder if that is the solution to the problem i am having with hesitation. I have checked everything to no avail....hmmmm

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MikeInAZ

The distributor pickup coil is one of the most overlooked problem causing components there are, probably followed by the CTS and MAF.

The pickup coil has a paper wrapping that gets brittle with age.

Just like points that won't run at low rpm but do fine at high rpm, fouled plugs that do the same, I don't know why but I've always noticed that ignition problems show up more at low rpm than high rpm.

RGZWS6

Very interesting! I'm having almost the same problems with my 86 TBI 2.5 Iron Duke. I know there are some differences but I have an 89 Foemula with a TBI and there are a lot of simularities.

I threw just about every sensor the car would take at it and still had the same problems as mentioned above. I thought that if the coil were bad surely the thing wouldn't even run let alone start. I have an idle problem that I need to give a little gas to solve. Runs like a champ around town but has an intermitent (sp) hesitation off idle. A replacement pick-up coil is only 4.99 so that will be the next part to buy/try

FWIW, Thanks!

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89 Formula 305 TBI
160* Stat, 200* Fan Switch, K&N Open Element, Headers, 3in Flowmaster, Pullies, 1.6 Full Roller Rockers, B&M Trans Cooler, Wonder Bar

3.73 Richmond Gears & SLP Zexel Torsen Posi ----Still Waiting To Install----