My '94 Deville has a small off-idle stumble. When you give it a bit of gas, it goes forward, stumbles for a half a second, then goes. It's real quick when it happens, but very noticeable.
Any ideas? There are no codes present.

i have had the exact same issue , it helped when i bumped my timing forward 3 degrees . i still have a stumble takeing off from the lights after im moving (3/4 way thru first gear) on normal take offs

My problem is only right off-idle. At all other throttle positions, the car runs great!

well you might consider bumping the timing forward 3 degrees and only running permium (im sure you do already)

that might just take care of it

By the way what is your reading on the pd04 in "pcm data" in diagnostic mode ? just curious on what your water temp is .....

I haven't checked the timing, so I guess I should at least see if it's within factory specs. I do run 93 octane in it.
The water temp runs around 96-100c. I had a problem with it a while ago overheating, but that was just the overfill hose being clogged causing the coolant to go into the tank, but not back into the radiator, so I had an empty radiator! Very strange problem, but it's been working fine for a month now!
But ever since I bought the car in May, it's had the slight off idle stumble.

reason i say about the timing is im thinking over time these distibutors get a little loose and just off idle the distributor isnt at factory sepcs becuase of some play in it . bumping it forward 3 degree helped the stumble quite a bit to where i dont really have it . i hear it makes a little more power too but i dont feel anything diffrent

Bumping up the timing will help add a little more power and torque. You will have to use premium fuel all the time to prevent spark knock. But....you shouldn't have to do this to correct a stumble. The engine will not stumble if it is working correctly...something is wrong.

I would check the EGR system. Clean the EGR tubes specifically. Hold the throttle wide open (engine off) and look down the throttle bores with a strong light. See the two tubes sticking up at you from the bottom of the intake manifold floor beneath the throttle plates....??? Those are the EGR tubes and they are not supposed to be plugged up with carbon. Rod them out thoroughly with a piece of stiff wire so the EGR can flow properly and likely your stumble will disappear. Without the EGR flowing correctly the engine is momentarily lean when you tip in because the ECM leans the mixture as it turns on the EGR to compensate for it. If the EGR flow is not there (due to plugged tubes) then the engine will stumble. Should be a simple fix.

hmm , i cleaned my out i think , but just the tubes to the point they curve sideways to meet up with the valve , also reaplaced the valve ...is there any way to clean the system and be 100% positive all carbon has been removed ? i used a wire coathangar in my case.....

is it possible to have a restricted egr system in between the tb tubes and the valve and no ping ?

The tubes themselves are straight and not curved. The open up into a passage beneath them that curves over to the EGR valve. You can take the EGR valve off and blow thru the passage and see that the air come thru the tubes under the throttle body. That would indicate that the passage is open. If the engine is idling and you reach under the EGR valve itself and gently pull up on the diaphragm that actuates the valve does the engine stumble and almost stall?? If so, then the EGR system is likely fine and capable of flowing EGR. Have a helper power brake the engine lightly against the torque converter while holding the brakes with the engine good and hot. Reach under the EGR valve and touch the diaphragm while the helper does this. You should be able to feel the EGR valve diaphragm quiver and open when the EGR applies. If the diaphragm doesn't move then the EGR is not turning on. It could be the vacuum source to the EGR solenoid or the solenoid itself. A vacuum gauge would tell you where the vacuum is missing. If the valve is getting vacuum and is still not opening then possibly the valve is wrong or failed.

ah ok , then it must be fine , it did indeed flows compressed air well and the valve works fine (did your test a few months ago) so i guess it is fine .....Just had that feeling maybe i didnt get everything ...

BTW its on a diet of delvac and that 4.9 just loves it , many thanks for that info ,shes never ran quieter or smoother

I sprayed some carb cleaner down the TB when I first bought it, but haven't checked the EGR tubes. I will do that and see if that helps.

A few other wierd quirks of my car:

The brake pedal will go softer once in a while, almost like the vacuum boost is kicking in more, because the car will decelerate much quicker than it was. It brakes fine, but just does this once in a while. I'm guessing a vacuum booster problem?

On start up the engine makes a noise for 1-2 seconds sounding like dry main bearings. It makes no noises any other time, just at start up. I hope it's nothing major and just a 4.9 quirk. :cookoo:

Thanks for the help! :worship:

I sprayed some carb cleaner down the TB when I first bought it, but haven't checked the EGR tubes. I will do that and see if that helps.

A few other wierd quirks of my car:

The brake pedal will go softer once in a while, almost like the vacuum boost is kicking in more, because the car will decelerate much quicker than it was. It brakes fine, but just does this once in a while. I'm guessing a vacuum booster problem?

On start up the engine makes a noise for 1-2 seconds sounding like dry main bearings. It makes no noises any other time, just at start up. I hope it's nothing major and just a 4.9 quirk. :cookoo:

Thanks for the help! :worship:


The carb cleaner didn't do anything.....LOL.

Clean out the EGR tubes as described.

While you are in there find that can of carb cleaner and spray the bores of the throttle body below the blades and scrub them with an old toothbrush. Clean the deposits off the back of the blades also. Disconnect the battery negative cable for 60 seconds to reset the idle learn offsets to account for the clean throttle body. Your idle speed control will like it.

well i got a 91 deville and have that same problem, maybe its cuz i run regular? but iono its not worth the extra 5 bucks to get off the line quicker. but would the stp fuel cleaner additive work to help solve this problem?

well i got a 91 deville and have that same problem, maybe its cuz i run regular? but iono its not worth the extra 5 bucks to get off the line quicker. but would the stp fuel cleaner additive work to help solve this problem?

NO, not likely.

I sprayed some carb cleaner down the TB when I first bought it, but haven't checked the EGR tubes. I will do that and see if that helps.

A few other wierd quirks of my car:

The brake pedal will go softer once in a while, almost like the vacuum boost is kicking in more, because the car will decelerate much quicker than it was. It brakes fine, but just does this once in a while. I'm guessing a vacuum booster problem?

On start up the engine makes a noise for 1-2 seconds sounding like dry main bearings. It makes no noises any other time, just at start up. I hope it's nothing major and just a 4.9 quirk. :cookoo:

Thanks for the help! :worship:

i also have the noise at startup , im thinking its some deal in the lifters or something , prolly normal , dont know why tho i only use GM filters so it cant be a drain back issue on the filter , maybe perhaps the lifters arent sealing up good after they get age and miles on them????

i've had a lifter knock at start-up ever since i bought the car almost 3 years ago (1991 seville).

The carb cleaner didn't do anything.....LOL.

Clean out the EGR tubes as described.

While you are in there find that can of carb cleaner and spray the bores of the throttle body below the blades and scrub them with an old toothbrush. Clean the deposits off the back of the blades also. Disconnect the battery negative cable for 60 seconds to reset the idle learn offsets to account for the clean throttle body. Your idle speed control will like it.

Well, the carb cleaner cleaned off the butterflies! But I will try to clean the EGR tubes today, and see what that does. I did use to toothbrush and cleaned out the TB a bit a few months ago.

but if u clean it all off, wouldnt it be bad if the deposits got into the motor?

ok well i just cleaned the egr vavle. its the thick ones sticking straight out from the bottom right? well the front one wasn't that bad but the one fartest away was clogged pretty bad. i started it up and it idled alot smoother. it still stumbles, i need a new isc motor, but this seemed to help alittle. thanks for the advice.

but if u clean it all off, wouldnt it be bad if the deposits got into the motor?


It does, but then it gets burned and blown out through the exhaust.