F-body-fan

Hi Guys, As some of you know I have been trying to figure out a chronic problem that my all stock 1987 5.7 camaro has. The problem is only at cold start ups. Car sitting for 5-8 hours in 60-70 degrees. The car will fire right away & hit the taget 1000 rpms for just a moment, but then drops sometimes below 500rpms & just barely clings to life. After about 8 seconds of this, it recovers again & jumps back up to 1000 rpms. From then on, it will start, run & drive absolutley perfect. This only happens when the engine is at room temperature & sitting for many hours. Even if I shut the engine off right after the first 10 seconds of running rough, & restart it an hour later, it will start normal & run smooth.

Here is a video of the start up: http://automationsystems.ws/images/5.7stumble.wmv

Now, Last night I have made some headway, But really need some opinions from here. It appears to be fuel related & this is my check list so far.

*fuel pressure at the rails is at 45lbs prior to start up & holds at 45lbs through the start up & when its idling smooth.

*Cold start injector is working well. Tested with a noid light & appears to function until 100+ degrees durring crank. This is also what seems to give the car the initial jump to 1000 rpms right after it starts.

*fuel injectors are all showing 16.2-16.5ohms CSI at 4.2ohms

*The IAC has been replaced, throttle body cleaned & the IAC counts set to 15 when the engine is hot. TPS at 52

*while this stumbling is going on the ECM is frantically trying to keep it running by opening the IAC to as much as 150 counts. As soon as it smoothens out, the count drops to under 60 & continues dropping as it starts to warm up.

This morning I opened up the front of the air intake box. Started the car cold & gave it two very small shots of starting fluid into the throttle body.
Guess what? It idled perfect, never stumbled, & those two little sprays where just what it need to get past those 8 initial seconds seen in the video.

Soooooo, now I am realizing that it would appear that its just not getting enough fuel for those first stumbling seconds. What can cause this? And why is it only when its been sitting for many hours?

Thanks for taking the time to read my post,

DENN_SHAH

iTrader: (1)

sounds like you may have intake valve deposits.
after sitting for a long time any fuel in the deposits evaporates.
then when you first start it after sitting the deposits absorb too much of the fuel being injected. until the deposits are saturated with fuel the motor is too lean.
the only ways to actually check for deposits on the back side of the intake valves is to either pull the complete intake or use a bore scope. if you have really god eyes, you may be able to pull the runners on one side and see the back side of the valves.
fortunately you can get some fuel additive for the tank to dissolve the deposits.
one that i've used with good success for this problem is BG 44K. the problem with BG products is you can only get them from an auto repair shop that carries the BG product line.
i've never used it, but seafoam or some of the other chemicals may also work good.

F-body-fan

Thanks for the idea! I do have an LED lit borescope with LCD monitor. The car has done this for a teribbly long time. basically quit driving it in 1996 And it did it back then. I have only put about 600 miles on it in that time frame. It has 62,xxx mile today. I quit driving it in 1995 because it developed a really rough idle & would stahl out. I monkey'd with a bunch things back then, & eventually found the distributar shaft lost its magnatism causing a misfire at low idle. At somepoint around that time is when the hard start happened. I have always figured it had something to do with my messing with the timing & idle speed screw. I had quit drivng the car at that point & just never let it bother me. Now that I am trying to figure this out, I am realizing its a seperate problem & has nothing to do with my "tweaking" 15+ years ago.

The inspection should be an easy one & its a great idea. My scope has a long enough reach to go past the throttle plates & find their way to the intake valve. If I can, I will see if I can post some pictures of my findings.

TTOP350

iTrader: (8)

Do you have the stock chip in it?

F-body-fan

Ttop350, Yes, its the stock chip,

UPDATE::

I might have found something, that could have been so obvious I never checked.
While looking to see if I could sneak my borescope down the runners to look at the intake valves, I was peeking at the EGR, & for grins & pulled the vacuum line off & plugged it. For the first time in who know when, the car started up after sitting all night & seemed to start perfect!!!!! I will test it again tomorrow morning & see.


Is it supposed to do that?? I am thinking not. Thought it should only function when under light load, crusing at normal operating temps?

F-body-fan

Well, went through the EGR & solenoid, & it would appear thats all working fine.
Had the system bypassed this morning, & still had the rough start. Dang, thought I was on to something.... Still scratching my head. Tried to slide my scope into the runners through the throttle body to look at the valves, but Too many twists & turns to do that without pulling the runners. So, for now I am putting that check off. Its just so strange how it recovers like a flip of the switch.

IROCgiraffe

iTrader: (3)

Any luck?

F-body-fan

Sadly, No........


This car pretty much spends its time in storage, So I only think about the problem when I pull it out to wash it, etc. For as long as I have owned this car, I think it has done this stumbling after sitting for a day or so.

The only thing I can think of (I think it was also mentioned above) Is to change the fuel pump. Just maybe air is somehow getting into the fuel rails & causing an iratic fuel injection when first started? Ive been over all the basic stuff. The car is completely stock & has low miles (62K) Years ago, I never used to let it bother me because it was only on the first start up of the day. But now days it drives me crazy....

The car can sit for 10-15 hours & it will not ever stumble. ITs only if it sits for over a day. Leaning towards thinkg its fuel related, but I just don't know....

jjcuff1

What about the O2 sensor? It sounds like with the warm up cycle then runs fine it is an open loop issue? Could your o2 be fouled. I had this on one car it tested fine (the o2) and did all other fixes but still had rough starts but ran fin. I replaced the o2 and wham. the o2 got 'stuck' high voltages so when running it was not noticeable but at idle it forced open loop or read it was always rich and therefore ran lean.

And I had no bad o2 light or sensor trip either. it was just process of elimnation

Joe Tag

iTrader: (4)

Did you ever actually pull the IAC valve or EGR? Its pretty common for carbon to build up on them and prevent them from fully opening or closing. Easily fixed with a can of carb cleaner if that's the issue

TTOP350

iTrader: (8)

Do you have K&N filters? Is the MAF wire clean? MAF good? Burnoff/power relays new?
Hot fuel in the rails when it sits?
Almost sounds like the 02 sensor is starting to kick in a bit to soon.

F-body-fan

Thanks for all the ideas guys. I did check the IAC & EGR last time I worked on it & couldn't find anything there. Problem is, with the car put away I don't have easy access to it. This summer I will bring it home again & look deeper & do more testing.

Thanks again, & I will lite up this thread again come summertime!!

OldAndInTheWay

iTrader: (1)

Do you have K&N filters?

Would K&N filters cause this? I'm having a similar issue and i have those filters. Seems to me I put them in around the time this started. Maybe I'll pull them and see what happens

TTOP350

iTrader: (8)

Only if the oil from the filters is covering the MAF wire.

F-body-fan

It has the stock filters, in fact I think they might be 15 years old. lol. But, they are clean.
This has really been a life long issue with this car. It has done this for so many years & when I used to drive the car, it never really bothered me that much. Now that I am older & much more particular, it bugs the heck out of me. The only hope I really have at this point (in my mind) is that maybe the fuel pump is bleeding all the fuel back to the tank, & somehow allowing air in the lines, then when it pressures back up the air is trapped in the fuel lines? Probably not seeing its a sealed system, but it sure seems fuel related.

I will be bringing it home in the next month or so & I'll do some more testing.

OldAndInTheWay

iTrader: (1)

Ok, thanks I'll check that. I don't think that is it since the filters are brand new and i did not oil them. But the rough idle on start-up until the car is hot did start then. Probably just a coincidence and something else is screwed up. The car is throwing a code that the Coolant Temp Sensor is bad, but its not. Replaced it and its still throwing the code. Maybe its the wiring for the CTS.

OldAndInTheWay

iTrader: (1)

My car has only been doing it for a few months. Doesn't bug me too much but annoys the heck out of my wife who drives it sometimes also. Over the winter my 305 was swapped out for a 350 but it wasn't a problem for the first 1000 miles so I'm thinking its not that. I think we took care of all the things that have to be switched when going from 305 to 350.

F-body-fan

Thought I would revive my old thread as I have the 87 home again. Been quite a few years! Car is running & driving great, But Still has the same problem I never figured out. It's funny because I had to re-read this 9 year old thread so I could check what I had done in the past.
I forgot all of the things I did years ago to trouble shoot.

Still doing the exact same thing. starts at high idle for a moment & them stumbles around 500rpm's while the iac is opening frantically to keep it running. sometimes it stalls, sometimes it hangs on & then gets to 1000 rpms, drops down & runs perfect.

I have a feeling its related to fuel. Maybe the fuel pressure regulator or the pump is allowing fuel to go backwards after siting & incidentally allow air from the tank into the rails? Not sure if thats even possible. I wouldn't think so, but maybe?

While I am pondering that, I do have a question though on the air control valve. should it go to "0" steps when the throttle is opened up, or does the ecu just leave the iac where ever its at when it sees the tps/throttle blades are opening? This would make sense to me that it would just stop adjusting, rather than closing so that a normal idle speed is ready & waiting when the throttle is returned?

KR81

Sorry to dig up an old post but did you ever solve this ? I've had the same issue for as long as I can remember.

F-body-fan

No worries & funny you revived it because I am hoping to get the car back home to work on this issue
Cant believe I started working on this 12 years go. Geez.

2 years ago I was trouble shooting again & followed one of Vaders write ups on setting minimum air on the throttle blades.
I had never done that with this car & decided to. the throttle blades were literally closed. I had to open them up quite a bit to get it to idle at 500. After setting the TPS with the new throttle position, the car was starting up cold & running dang near perfect, But it was throwing a code 34 within
seconds of starting. I believe that was the code for low voltage from the MAF. I never got any further. That fall got busy & the car went back into storage.

I will hopefully get back to this soon & see what I can figure out.

Have you set the minimum air speed on your car? Its doing the same thing with a rough first start, & then its good?

erik69&85

iTrader: (1)

Let me throw this out there.... If the throttle plate position at idle is opened up, the MAF will read less air than the TPS would imply based on the feedback to the ECM. After setting the idle airflow, did you check that the TPS is showing min voltage?...you may need to reset it's position.. if it's not at min, it's telling the ECM that the throttle is opened.... I think a mismatch between MAF flow and TPS feedback can throw a code 34.

I was getting this in my 88... Caused by the mismatch...

KR81

I have done Vaders write up and set it all properly, still get it 😫
Yeah literally only the very first cold crank. If it does infact stall on that first crank I can try again and it'll fire right up no issues at all. It can get a bit off sometimes when warm, not quite as bad but still just a bit of a sloppy/lazy kind of start up if you get what I mean but for the most part will start satisfactorily the rest of the day, regardless of how ever many hours later, it'll only do the real bad rough start when it's left over night.

F-body-fan

Well, I am happy to report I can close this case & the rough start up / idle mystery has been solved. It was difficult for me to figure out as it was a true coincidence of events. In general, I am not usually a believer in coincidences when it comes to trouble shooting things, but this time it was.

This started out as just wanting to cure the rough cold start idle my 87 had for decades. 1996-ish to be exact. I had tried setting the throttle blades with iac counts over 10 years ago & it changed nothing. For anyone who read my post above you will see I was starting to be convinced I was getting air into the fuel lines after the car would sit for a while, but sure glad I didn't rip out the fuel pump as that would have been a big dissapointing mistake.

Then I stumbled onto Vaders write up last year & decide to give that a try last summer. To my surprise, My throttle blades were way too far closed. I had to turn them open quite a bit to get the car to idle at 500 rpms with the iac closed. Once I had them adjusted & plugged everything back in all seemed good at first, but the next morning I went to start the car & it started throwing maf voltage codes. I figured it had to be something with what I had adjusted because I have always found most new problems are the effects of what you last touched.

I tried another MAF from another car, with no change. Then followed the MAF trouble shooting chart & all tested good with a test light. Back probed the MAF wires & had the correct voltages. Hmmmmm, So I figured maybe the ECM went nuts from having the iac unplugged during my previous adjustments. Purchased a used ECM & no change again. Car went into storage again last fall. So this year I put a lab scope on the MAF wires & started it up. What I saw was fast fluctuating voltage jumps & dips in the 12V power which of course was effecting the voltages in the data wire. I could see the same dips & spikes on that wire, but at a lower voltage and the spikes & drops were reversed. when the 12V would drop the reference voltage would spike. For whatever reason I was not seeing that on my voltmeter, but could see it clear as day in a 500ms scale on the scope. Traced it back to the relay. Even though the relay by itself tested good, it was clearly failing. I cleaned all the connections & installed another relay & boom. No more codes or rough idle. Voltages where steady.

I then went back to where I was at last year & started over with the min air setting procedure with he throttle blades. Once that was done, I waiting a couple of days & started the car again not sure what to expect. Started & ran perfect! Not a stumble or hesitation whatsoever.

So my problems clearly started out as just a minimum air setting issue, but became complicated with a MAF issue right at the same time of adjustments. Seems like crazy luck & it really clouded my thought process.

For what its worth, my car seem to have an iac that is very low at hot idle. usually around 4-5 steps My iac was getting my car to idle before, but the cold starts, there was just not enough air. Thats why this car started hard for so many years.