1991 Seville 4.9L Engine Stumble (TECH PLEASE)

[cjhudson87]

Hello Everybody!

I just purchased a 1991 Cadillac Seville with the 4.9 liter engine and 116,000 miles on the clock. This car is awsome and it runs really well...except for a little stumble.

Here is the description of the problem:

On cold start...the engine stumbles noticeably on initial engine startup as the rpms increase. As the rpms settle back down the stumble becomes less intense, but it still bucks intermitently while at a steady idle.

On acceleration...the engine stumbles/bucks on tip in acceleration. It only does it on extremely small throttle openings. Anything past 1/4 throttle and the stumble goes away.

At constant speed cruise...the engine stumbles/bucks during cruising when steady, small throttle opening conditions are present. Climbing a hill or coasting with the throttle valve closed eliminate the problem.

Consequently, I just had the car smogged and it passed with flying colors. I wasn't anticipating the car passing, in fact I had only taken it in to see how it was running, hoping that could point me in the direction of the stumble. NOX was particularly low. The car was bucking like crazy on the dyno and I never thought it would pass...it sounded like hell.

The only other thing that I can think to include here is that I tried to disconnect the vacuum hose going to the EGR (thinking that it might be sticking open) and the bucking seemed to stop, but was replaced by a terrible knocking noise that didn't go away at any speed. I replaced the vacuum hose almost immediately.

Anybody know what I need to do to make my car drive like it wants to?

Thanks,
Casey Hudson

[sint3k]

From your description it could be a number of things all ranging from the simplest to more complicated. For the idling it could be the Idle air controller but sence your having these problems at part throttle it could be spark plugs , wires , ignition coil. Find out the codes and post them on here and i'm sure someone will be able to help you more.

[carnut]

First thing I would do is clean the throttle body intake at the throttle blade. Remove the intake air hose and spray the throttle blade with either throttle body cleaner or Brakeclean. Hold the throttle blade wide open, spray and scrub with a toothbrush till its clean.(throw away toothbrush!!) Will be hard to restart and run rough for a few seconds, then should smooth out. You make no mention of checking for fault codes. Are you familiar with how to do this? Do a search for "fault codes" and report back.

[cjhudson87]

Will I have fault codes without a check engine light?

How do I check them?

Thanks!

[carnut]

Yes, you can have stored codes. At the top of this Eldo, Seville forum is a sticky describing how to pull codes.

[awadecki]

Hang on, there. IF your stumbling goes away when you remove the EGR vacuum hose, the EGR is probably your issue. Yes, clean the EGR tubes out in the throttle body, but the valve is probably sticking. Try this: 1) Disconnect EGR vacuum hose, 2) Hit the top of the EGR with a wrench a few times, 3) Drive the car. If the stumbling goes away, that's your problem. Do NOT drive far with the vacuum hose off, as you'll experience "pinging". Replace the EGR and vacuum hose.

[carnut]

Also, at idle there should be no vacuum present thru this hose to the EGR.

[cjhudson87]

Originally Posted by awadecki

Hang on, there. IF your stumbling goes away when you remove the EGR vacuum hose, the EGR is probably your issue. Yes, clean the EGR tubes out in the throttle body, but the valve is probably sticking. Try this: 1) Disconnect EGR vacuum hose, 2) Hit the top of the EGR with a wrench a few times, 3) Drive the car. If the stumbling goes away, that's your problem. Do NOT drive far with the vacuum hose off, as you'll experience "pinging". Replace the EGR and vacuum hose.

What is the reason for hitting the valve with a wrench a few times?

If the EGR valve is my problem is replacing it the only option, or is it posible to clean it?

[cjhudson87]

Ok...so I pulled the codes. Here's what I got:

"E030-ISC RPM Out Of Range"
"E052-PCM Memory Reset (See Note)" <---what note?
"B121-Twilight Enable Switch Circuit"
"B122-Panel Dimming Switch Pot Circuit"
"B123-Courtesy Lamps Panel Switch Circuit"
"B447-Low Refridgerant Pressure"
"B552-Keep Alive Memory Error"

and last but not least code "R061" which I can't find in the sticky. The only thing I can see applying to my problem is the "E030-ISC RPM Out Of Range", but I am not sure how to address that. Furthermore, I couldn't get the code clearing techniques outlined in the sticky to work. Any pointers there?

I gotta say that I am very happy to have found this resource and I really appreciate all of the help that I have been getting. You guys rock! Thank you so much!!!

[carnut]

I think the majority of these codes are "history" hence no current SES light. Its worthwhile to erase ALL the codes then drive it. Believe me, if the problems are current the light will come on and the codes will reset. Regarding erasing codes, think of the hi fan button as saying yes, the low fan button as saying no to the computer. So once the display says ECM? hit the hi fan to say yes. It then will display various things to do, one being erase codes? Then hit the hi fan button saying "yes". It should then say codes clear. Hit the "off" button, it will go to the next segment check. It will go thru ECM, BCM and SIR displays. Each can be answered either yes or no to progress thru the messages. Once you feel all codes are erased, shut the car off wait 10 seconds, restart and re enter diagnostics. You should see "no ECM codes'" etc. Most ISC out of range issues have to do with either adjusting the ISC or cleaning the throttle body because the ISC is trying to correct the idle by over extending. E codes are ECM, B codes are BCM and so forth.

[cjhudson87]

Originally Posted by carnut

Most ISC out of range issues have to do with either adjusting the ISC or cleaning the throttle body because the ISC is trying to correct the idle by over extending. E codes are ECM, B codes are BCM and so forth.

I did clean the throttle body...quite thoroughly in fact and it didn't seem to help the situation. Anybody have any idea what that "R061" code is all about?

I tried to disconnect the EGR vacuum hose again...it seems like it gets better, but I can't tell if it really does because it pings so bad. Can I clean the EGR valve, or would this have no effect?

Finally, I haven't done a tune up yet. I was trying to save some money. My rational for not doing it was two-fold. One, the car passed smog with flying colors, and two, if the problem stemmed from a bad plug, plug wire, or cap/rotor shouldn't it get worse with increased engine load/rpm?

Again thanks so much. I will continue to post my findings and the results of reccomendations. Thanks!

[carnut]

I have to say I have limited working knowledge of this engine, but there are many posts here that speak to cleaning the EGR tubes under the throttle body. But I would think these are ok on yours because the EGR seems to work. Does not ping hooked up, pings disconnected. R codes deal with suspension I believe, not driveability. Thats why its important to separate history from current codes.

[cjhudson87]

Update:

I cleared codes and I drove the car, experiencing the stumble (you know, bucking is the more appropriate way to describe what the car is doing) for a good portion of the drive. I operated the car throughout the rpm range, but concentrated my driving where the problem was most pervasive hoping to trigger a code. I did not trigger any idiot lights while driving and upon returning home, pulled codes again to find one, "B123-Courtesy Lamps Panel Switch Circuit", which obviously has nothing to do with my problem.

I did stumble accross something interesting while clearing my codes however. While attempting to figure out how to clear codes I accidentally found myself in a portion of the computer that allows you to address individual vehicle systems. While there I went into a TPS function which measured the voltage of the TPS at different opening levels. The baseline TPS voltage reading (pedal out) was 3.3 and with the pedal at the floor the reading was 76.3. I then started the car, remaining in the same screen and noticed that at idle the TPS voltage dropped to -0.2 and the car was stumbling very bad. I proceeded to increase the amount of pedal until it cleared up, which just so happened to occur at a voltage reading of 3.3, the same reading as the baseline with the motor off. Could this just be a Coincidence, or does this indicate that the TPS may be my culprit?

Thanks Again!

[cjhudson87]

Can anybody tell me what the TPS angle values should be with my car RUNNING at idle?

I am seeing 0.2...I thought I saw somewhere where it said it should be 3-4.

[awadecki]

the reason for hitting the egr with a wrench is to free the diaphragm. if it becomes sticky, this will free it. your symptoms sound like a sticking egr. it will cause hard starting and stumbling.