Lt1 stumbles when cold
Thread Starter
Instructor
Joined: May 2014
Posts: 237
Likes: 0
From: Florida
Lt1 stumbles when cold
When I start the car before it is warmed up, the engine will stumble. This happens with the ac on or off and accelerating up only makes it worse. It just happens when the idle comes down. It will come down to like 500 then pick up, revs fine, come down and pick up to normal idle. Makes it difficult with a stick. After the engine warms up some, it disappears. I think it's messing with my mpg too because I was getting better mpg when I first got it! Air filters were just cleaned, I looked at the maf and it doesn't look bad but I could be wrong, and there are no obvious vacuum leaks...
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
What is your TPS voltage? I would try a minimum idle reset first. After that, what is your MAF gm/sec at idle? At 1k, 2k, 3k RPMs? Maybe you can have someone nice enough with the same car to compare your results for you. I'd probably lean more towards the MAF in this case, but I would also check for a vacuum leak using multiple methods. Get a cigar, suck in the smoke and blow it into one of the bigger sized vacuum lines. If smoke comes out anywhere you know where the leak it. Anything after the MAF sensor would be a vacuum leak. Spray around the intake with carb cleaner or starting fluid. If the idle rises you found your leak. Do the same thing with an unlit propane torch. Also, post the results for your MAP sensor at the same RPMs, and possibly go for a WOT run too and report the MAP data too. Put a fuel pressure gauge on your car too and report the fuel pressure at idle, normal driving, WOT, and when the stumble happens. You can route the gauge up through the hood and onto the windshield.
Thread Starter
Instructor
Joined: May 2014
Posts: 237
Likes: 0
From: Florida
Ok I have not checked my tps voltage yet. would that just be checking it with the key to on? are there 2 different prongs or 1?? I have no idea what you mean by my MAF gm/sec nor do I know how to report my MAP data. I have no datalogging system or cables but I do have a laptop. I am taking the car to my work over the weekend for something else so I guess we will see what else I can do.
Burning Brakes
Joined: Mar 2005
Posts: 800
Likes: 2
There is no minimum idle procedure for your LT1. That is all controlled by the PCM. The tps usually throws a code as that too is not adjustable on the LT1 cars without modifications. Depending on year you may not even have a MAF. What I would do is pull the IAC valve and clean the throttle body real good and do the IAC reset procedure. If memory serves that is depress the throttle slightly and start car, when car fires let off the throttle and allow to run for 5 seconds, cut key off for 10 seconds and restart car.
Burning Brakes
Joined: Mar 2005
Posts: 800
Likes: 2
Yours is 94 or newer then? The only gasket would be for the throttle body if you remove it, and either an o-ring or a gasket on the IAC valve. My 93 is a gasket but that could have changed
Le Mans Master
Joined: Dec 2006
Posts: 5,154
Likes: 2
From: Ft Myers Florida
Had similar problem on my 94, turns out it was soot in the maf sending incorrect temp reading. Take the snap ring out that holds the screen in, take out the screen. Use a fine hair brush like a model brush and clean the resistors in there, if they are black they are covered.
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Thread Starter
Instructor
Joined: May 2014
Posts: 237
Likes: 0
From: Florida
so I cleaned the maf yesterday. I cleaned both the inside metal which wasn't dirty but it had minor green buildup and then the external air meter which was dirty. no change. i do think it'll only do it if the ac is selected on. it actually died on me and i had to restart it.
Last edited by Hairy W Bush; May 11, 2014 at 04:12 PM.
Thread Starter
Instructor
Joined: May 2014
Posts: 237
Likes: 0
From: Florida
guys this morning i had to jump the car and now it's 10x worse to the point where it does it ALL THE TIME. it only comes back to normal if i let it idle for at least a few seconds. what do i do?? do i need to do an idle reset or iac reset or something?? please help asap i need this car.
Last edited by Hairy W Bush; May 13, 2014 at 01:25 PM.
Thread Starter
Instructor
Joined: May 2014
Posts: 237
Likes: 0
From: Florida
yes I tried pulling codes from the ac control center and it shows I am clear. my fpr actually is not holding a vacuum and the line has a little fuel smell so now I have 2 ways to fix but I am afraid of pulling the iac and messing up whatever adjustment there is on it. because you said i should pull it and then clean it...
Last edited by Hairy W Bush; May 14, 2014 at 10:16 AM.
Thread Starter
Instructor
Joined: May 2014
Posts: 237
Likes: 0
From: Florida
just replaced the fuel pressure regulator with a brand new one that DOES hold vacuum. It still seemed to do it. I then did eatmydst1234's suggestion of the iac reset procedure and it's still evident. I have not driven it however.