IrishGreen

I bought a 91 Camaro RS with a 305 TPI and auto transmission for my son and I to fix up. We got lucky and found one with only 48,000 original miles and was literally owned by a little old lady since new. The vehicle is completely sound. Never wrecked and once we put in a new battery it started and ran perfectly. However; now it has developed an erratic idle. It will start normally and then go from 2000 RPM's to 500 RPM's until it ultimately stalls. I replaced the MAP Sensor, cleaned the IAC valve and checked for any air leaks. It is very frustrating. The car looks factory new and doesn't knock or blow any smoke. Could it be the O2 Sensor, EGR Valve, simply a bad fuel filter from 2 year old gas? My boy and I are stuck. Please help!

five7kid

iTrader: (14)

Welcome aboard thirdgen.org.

Sounds like a great find, and a good father/son project.

I'm going to move this to the TPI forum, as I think you'll get more useable answers there.

racerx520

iTrader: (1)

IMO, no hurt in giving it a tune-up....new cap/rotor, plugs, wires, thermostat, fuel filter, the works.

paulo57509

I vote for bad fuel. Open the filler cap and give the pipe a sniff. If it smells like paint thinner you've found the problem.

rdhanded2

iTrader: (3)

check coolant temp sensor also. Might as well change it in the tune up.

IrishGreen

Thanks for the suggestions. I will try them out this weekend. I also heard that a TPS could cause this but is more rare in a car with such low miles. Any thoughts?

Jonesyfxr

iTrader: (2)

First off...great find and welcome!!

Secondly, if you keep your foot in the gas until the car warms up will it stay running? Sounds like a vacuum leak.....possibly from a stuck EGR.

Are there any codes?

Oh.....BTW....where's the pictures? Lol

Tuned Performance

iTrader: (92)

With two year old fuel in the tank, you need to go through the entire fuel system, fuel pump, filter and call up southbay fuel injectors and get a set of there bosch 3 19#hr injectors. It would be a wise idea to even replace the fuel pressure diaphragm.

RBob

iTrader: (1)

A '91 RS would be either a 5.0l TBI setup or a 3.1l MPFI set up. If it truly has a TPI on it then it was swapped on.

RBob.

IrishGreen

I attached some pictures. We are certain the car is completely original as it came from GM. No modifications at all. I did make a mistake about it being TPI. It is a TBI as you can tell from the pictures. We have never done a project like this so we are still learning. Keep the suggestions coming. I appreciate them all.

Jim85IROC

iTrader: (2)

That's TBI (throttlebody injection), not TPI (Tuned Port Injection). Perhaps a moderator can move this thread (again) to the correct forum.

Jonesyfxr

iTrader: (2)

Tuned Performance won't steer you wrong.

I concur with him also, as old fuel that smells like turpentine is BAD and won't burn correctly.

If you need to drain a tank you can either syphon out the gas or disconnect a fuel feed line and power up the pump to push the fuel out. Then fill with fresh fuel. A can of Seafoam winter hurt either.

IrishGreen

If I keep the motor running at high RPM's it will run, but it is a struggle. Also it seems that the exhaust has a really rich odor to it. That may be my imagination, but that's what it seems. I have not obtained a code reading yet, hope to do that this weekend.

Richboll

I'd also be checking all of the vacuum lines for a cracked or split line. That can also cause the motor to surge.

IrishGreen

Checked all of the vacuum lines last night. And they all seem to be in great shape. I was able to pull a code of "12" from the computer by jumping the pins. I am planning on putting in a new fuel filter this weekend (well actually my boy can do that, he needs to learn sometime). Also without the aircleaner on the car, the one TB port seemed to be sucking air like crazy. Is that normal when it is removed?

five7kid

iTrader: (14)

Gads, completely missed that.

Thanks for getting that straightened out.

ImBrandon

Check to see if your gas tank recall was taken car of. I think 91-92 Camaro's and firebirds had recalls on the tanks. Also a weak fuel pump can cause surging like that even if it revs up high.

IrishGreen

Update:
This weekend I jumped the pins and got a repeating "12" Code with the SES. I replaced the fuel filter. Brand new IAC (which I reset according to TGO). Brand new EGR and EGR selenoid as well as a new O2 Sensor. Checked every eletrical connection for erosion and every vacuum line for wear. Evrything checks out. Unhooked the battery and allowed the ECM to reset. Started the car and it made no difference. It still idles up and down until it stalls out. Absolutely no change at all.

What am I missing? It seems that people have solved this problem 100 different ways. I am a total newbie to the electrical system. Is it a fuel issue? exhaust? Vacuum? I am really confused on how to proceed from here. I cannot continue throwing parts on it anymore. Seems fruitless and wasteful.

Any help is greatly appreciated. I promise to continue this thread to its conclusion.

rdhanded2

iTrader: (3)

I just had this same issue and it was the coolant temp sensor. Replaced it and instant correction. The problem is so many sensors on these engines cause the same rough idle issues. Also, have you checked the timing? That is free and can cause this issue as well.

IrishGreen

Was the CTS hard to change? I have heard of that being a problem for others. I can check the timing this week.

rdhanded2

iTrader: (3)

Not remotely hard. Simple, just need a wrench and 2 minutes.

IrishGreen

I will replace that CTS this week. Thanks for the heads up. I was not aware that a timing issue would cause it to go up and down like that. I guess I will have to check for someone with a timing gun.

IrishGreen

Update:
Replaced the CTS today and the car (at first) had the same loping idle. I let it warm up and it seemed to start to level out a bit. I then unplugged the TPS while it was running and it leveled out into a nice even idle. High RPM, but at least even. I turned it off and it struggled getting an even idle again. I am thinking of changing the TPS, resetting the IAC, clearing the ECM and then seeing if it levels out and this problem is finally solved.

Any thoughts?

Neal301

Having the same problem, and atcually a few other people are too,

this question has been asked many times and nobody on these forums has ever posted a fix and I WILL if I ever find a solution. Ive moved my diagnosis from MAF>VACUUM>IAC>TPS>EGR>FUEL now I believe something is off with the fuel system. Nothings ever fixed my rough surging idle and nobody on these boards has ever helped. Sorry guy but your on you own when it comes to this unfortunately.

Neal301

https://www.thirdgen.org/forums/tpi/...sure-rise.html

https://www.thirdgen.org/forums/tbi/...i-surging.html

https://www.thirdgen.org/forums/tech...h-problem.html (my post)

https://www.thirdgen.org/forums/tech...-stalling.html

ReEntry Racer

I had this once in an '88 Formula.
The in-tank fuel pump had a soft/leaking hose joining the sock pick-up to the pump motor.
Replaced the whole unit, ran perfectly.

IrishGreen

I have not checked the fuel pressure yet and was hoping to avoid having to drop the tank. However; I believe I have narrowed it down to a fuel delivery issue. Since the car has so few miles on it I did not think the pump would fail. But I guess its always possible. My question is this; Once I finally get this fixed, how reliable are these cars? Will I be chasing ghosts forever?

TTOP350

iTrader: (8)

Buy a factory service manual from HELM INC.
It's worth every penny and you won't get a bunch of guesses.
You'll get a book full of info on how to properly test things so your not replacing good parts and wasting money by guessing.

morgsie

iTrader: (1)

You have a vacuum leak. TBI gasket, worn throttle shafts, disconnected MAP, leaking EGR valve or leaking EGR solenoid, etc etc etc. Good idea to upgrade to a 3-wire O2, I found even in 5*C weather that my car would go into open loop while driving at moderate speeds. Fuel pressure should be checked for sure, TPI pump is a good upgrade. I would highly recommend getting injectors cleaned (witchhunter). My Car would not pass emissions, i swapped in a used set from the junkyard and it not only idled better but passed emissions with flying colours. If I kept the car I would have got the injectors cleaned as the idle was still not 100%. You can pickup a TBI gasket kit for $35 off amazon. A local carb shop might be able to rebush the throttleshaft if it has excessive slop in it. Get this cable from moates so you can datalog. I used it for troubleshooting on my car and a few of my friends. A must if you don't want to be shooting in the dark when troubleshooting TBI.

ReEntry Racer

The car is fine. The pump is actually fine too. That pick-up hose is mush.
You need not drop the tank, which is a very big deal, with exhaust and rear diff being moved out of the way, etc. I can send you pictures of the access panel I cut in the floor above the tank, and the way I cut the rigid lines to/from the pump and reconnected them using fuel injection hose and gear clamps.
This was all done with a full tank of gas in less than a day, outside.

Caveman305

iTrader: (8)

i actually just went through a similar situation as this,

mine ended up being a split in the hose that connects the pump to the sender, the hose itself is only an inch or two long, mine developed a split from age, as far as i have read, its very common and causes the idle to hunt

if unplugging the map immediately remedies the idle issue i can almost guarantee it being that little piece of hose
easiest way to tell is to check fuel pressure, mine was reading just over 2 psi,
i decided to replace the entire sending unit with pump(bought drop in replacement), as soon as i fired the car up after install it was reading over 10 psi

dropping the tank is not as bad as people make it out to be, i had my tank out in 3 hours(hint, when removing the tank, drop the pass side down and swing it over the rear, not away from it)

if i had to do it again i could get the tank dropped and re-installed in under 3 hours

vidfuse

have you tried testing the Throttle Position Sensor it should have three wires. You will need make jumpers for at least 2. The one that sends the signal from the computer (+POS)and the one that returns the signal(NEG). Their is a voltage range I do not know what color wires you need to make jumpers for so maybe just match them up male to female. If you just buy a new sensor you will need to adjust it anyway.

Their are some specs here and directions here https://www.thirdgen.org/tpimod2
.54-75@ idle and 4.0@wot

Darren1

I had a surging problem. Changed parts till I was broke, checked for vacum leak three times. I ended up pulling the distributer connectors several times on/off on/off. and then Miranda purred like a kitty again. Guess it was just corroded connections. Not sure if that will help you but at least it is free to try. Good Luck

1991sleeper

iTrader: (-3)

My car had a similar issue ... It was the TPS sensor .... U can test it with a voltmeter set on DCV 20* .... U need to make 3 jumper wires about 3" long and insert one end into the TPS and one end into the plug on each wire with key off after your 3 wires are secure in both ends turn key on engine off and find the 2 wires that give u a reading it shoul be around .5-.7V with throttle closed .. And should gradually raise as u open the throttle in a linear fashion ... If it spikes up real fast or jumps around or just flat out don't give a reading it's bad

Oh and the TPS on the 91-92 TBI cars are NOT adjustable like the earlier ones

IrishGreen

I replaced both the IAC and TPS but the car seems to run even worse than before. I tried to adjust the IAC to minimum air using TGO specs. I cannot get the IAC to extend fully into the Throttle Body. Is it possible that the new IAC has broken already? From the symptoms it appears like an IAC or TPS problem. I know I am getting close, just can't seem to fix it completely.

rdhanded2

iTrader: (3)

edit

0oops... need to read! lol

11ellswray

iTrader: (1)

is it possible you replaced the parts incorrectly? check for vac leaks around the new iac and also check to be sure that the new tps is adjusted correctly

IrishGreen

My TPS is not adjustable. So I don't see how I could've installed it wrong. I've checked the entire engine twice for sit leaks. Found nothing. Going to drain he tank and put some sea foam in with new gas. Couldn't hurt.

IrishGreen

Update:
So I was playing with the vast array of new parts I placed on the car recently and unhooked the MAP Sensor just for "fun". The car was able to catch an idle. The idle was very high and the engine was running rich (exhaust smell was really strong). As soon as the MAP Sensor is plugged back in, the car goes back to searching for an idle. This car is possessed!!!!

Beginning to think purchasing this car was a huge mistake.

mikegolz1987

I had some issues like this I have a 91 rs 5.0 t.b.i I was ready to sell couldn't find the problem had rich smell and all and went spent money on parts like a dummy but with some tinkering one day pull the fuel filter off and it was trashed changed it out and she rund like a dream I did replace the fuel line from the filter back it was stopped up but now shes a champ again here Honda Honda Honda hope that helps good luck

IrishGreen

I changed out the fuel filter with a new AC Delco filter. The fuel in the tank is old but I think my next move is to test the fuel pressure. Not an easy task from what I have been reading.

kauboy

I'd check the TBI base gasket.

Caveman305

iTrader: (8)

Read my response from above, this is exactly what I described

Caveman305

iTrader: (8)

testing the fuel pressure is extremely easy on a TBI motor

buy an Actron fuel Pressure testing kit(or rent one) that has the GM TBI adapter

under the hood on the right side of the engine compartment towards the nose of the car you will see where the rubber line meets the hard line that runs up behind the alternator and to the TBI unit

put the adapter between the rubber and hard line, do not try to install at the back of the TBI unless you plan on keeping the adapter in place!

hook gauge up and prime the pump(primed mine reads just under 10psi, running the gauge reads just over 10psi)



changing the pump isn't bad either, i suggest changing out the entire sending unit and all rubber lines while you have it dropped, i got a sending unit with pump already assembled from Amazon for $115 shipped(Spectra brand)

tip for IF you need to drop the tank, the back end of the car needs to be lifted high, i extended my jack stands to their highest point, and when the tank can drop, it drops down on the pass side and swings over the rear end

IrishGreen

Well my next project is fuel pressure testing I guess. I have never done it before so it will be a learning experience. Then on to new plugs and wires. At least its nice and cold out.

armos

A car that's been sitting is highly prone to fuel system problems, so hold that set of components as primary suspects.
Definitely check the fuel pressure, both with key on engine off, and with engine running. I'm not sure about TBI but I know on port injection the fuel pressure regulator should cause the fuel pressure to maintain a constant differential versus manifold pressure.
After that test, turn the key off and keep watching the fuel pressure. It should hold pressure, leaking down no more than a few psi in 15-20 minutes. If it leaks down quickly then you have a leak somewhere. That might not be the cause of your primary issues, but it is something to watch for.

Bad gas in itself can also be a problem, even if it hasn't clogged up anything. You might never get it running right until all the bad gas is out of it.
You may have clogged injectors. Even if not, just because of the age of the car I'd be inclined to get them refurbished or replaced. Don't do that until you're convinced that the whole fuel system is clean though.

I fought with a surging idle for 2 years on a 2.8L Fiero. The problem turned out to be an incompatibility between the factory programming and the later model injectors that had been installed. It wasn't calibrated correctly for how those injectors behaved at short pulse widths (critical when idling). The fix in the end was to copy some parts of the programming from a later model car that those injectors matched up to.

I'm guessing your car has original injectors due to the low mileage, but I'd be highly suspicious of their condition.
I've heard of using a timing light to watch the spray pattern on TBI. I don't know if that test works on the F-Body or not, but I suppose it would.

Sensors:
I hope you kept your original sensors, because the factory originals are likely better made and more reliable than modern aftermarket parts are. Many sensors can be tested in various ways. They should be tested before being replaced.

Unplugging the MAP, or the O2 sensor, and possibly also the TPS (not sure about that one), will cause the ECM to run the car rich (it does this as a fallback when it detects sensor failure). The rich mixture can have the effect of masking the problem, but it doesn't always mean the particular sensor is actually at fault.

Unless the TPS signal is jumping around, then it shouldn't affect steady state idling.
Use a multimeter and verify you have a steady 5.0V feeding the MAP and TPS. Unlikely to be the problem but it should be checked.


Are you sure the base timing is set correctly? You have to disable ECM timing advance when checking timing, otherwise it will throw off the reading and cause you to set it incorrectly. I don't know what the procedure is on your car, probably a plug that needs to be disconnected. On a Fiero there's 2 pins that need to be jumpered on the ALDL connector.
If base timing was set correctly, then it should appear several degrees more advanced when you check it under normal operating conditions.

Caveman305

iTrader: (8)

The TBI system should not hold pressure at all, it's not designed too and only pushes 8-15 PSI stock

James Sutton

iTrader: (2)

What is your timing set at?

IrishGreen

UPDATE:
Well we went out and a bought the Actron Pro Fuel Pressure Kit at Autozone ($60) and tested the fuel pressure at the top feed line directly behind the alternator. The gauge was reading steady at 5 psi. Obviously very low. I pinched off the return line and the gauge stayed at 5psi (didn't even budge). So this appears to be a problem. I am gong to put in an AC Delco pump and sock as a replacement this week.

If this turns out to be the issue, I owe ReEntry Racer and Caveman305 a tall frosty drink. As they are the ones who told me about this exact problem. I will keep you posted as to the results of the new pump.

Also on the agenda for the car is new plugs/wires, new cap and rotor, coolant flush, new oil and brakes. My son and I have learned a lot working on this car already and we owe that to all of you. Thank you.

armos

Whoops, thanks for the correction.
Also, now that I think about it, TBI probably doesn't vary against manifold pressure either, since the injectors are upstream of the throttle plate. So that comment was also probably incorrect. I used to have a TBI GM but it was a long time ago.