Hey Guys,

I'm still having trouble trying to figure out whats wrong with me SSEI. Engine will idle very rough after a short warm up period.

I'll try to keep this to the point:

New plugs and wires
New fuel filter
New 02 sensor
New PCM (used but in working condition)
New PCV

Tested MAF and clean
Tested IAC and clean
Cleaned TP and TB
Cleaned EGR and lubed springs
Cleaned battery connections and PCM ground

Checked IAT
Checked fuel regulator
Checked vacuum leaks
Checked spark
Checked coils

No plug fouling
Fuel pressure at spec

I even had the dealer check it and they cleaned the fuel injectors. This did not improve the condition at all. I have run seafoam through as well.

Any ideas??

Unfortunately my 95 SSEI has the same symptoms. My checklist is identical to yours except I have not checked the fuel pressure. My scan tool says that it is the # 4 cylinder. I even replaced the LIM earlier this week. Pullled all of the fuel injectors, soaked them in injector cleaner and put them back in no particular order so I doubt that it is a bad injector since cylinder #4 is still showing up as the culprit. It could be a problem with the electrical input to the injector. I haven't tested that yet. I am going pull the plugs again tomorrow. I did not plan to piggyback but was actually logging on to ask the same question. It runs fine for a few minutes when cold but as it warms up it misses quite a bit. Seems to smooth out at higher rpm and is really strong at WOT. Oh, did not change out the PCM either. I doubt if any of this helps but I do feel your pain. You might want to get a scan tool on if if you haven't done so yet.

Hey Crece thanks for your reply. Yeah I'm pretty frustrated with this as well. What kind of scan tool do you have? I was under the impression that OBD1 didn't read any live data just codes, if that is not the case I might pick one up.

Have you done a compression test? That'* one thing I have yet to do but maybe that will help you figure out whats going on. Another thing is I think my SC coupler is going out but don't think thats related to the idle issue.

I use an Actron CP9145. They don't make them anymore but if you are lucky they can still be found. Here is a link that I found this morning and the price is good. Actron CP9145 Super AutoScanner - Deals and Prices You would need to order the cable specific for your vehicle. It should be around $25-$30 for the cable. I got the cable extender with mine also which is very useful. I haven't done a compression test yet. I just picked up a vacuum gauge tester yesterday so I will start testing this week. I have been told that it is probably a vacuum leak and I agree but I haven't been able to pinpoint it yet. I may be chasing a diferrent problem now though since I changed out the LIM. I had purchased o-ring kits for the fuel injectors but decided at the last minute that I might not need them. (pockets were getting a little light) Now I plan to look at the spray pattern, check for leaks and check the electrical connectors on the injectors then install the new o-rings. I doubt that your coupler issue is affecting the idle also but I did change mine along with the LIM and it is a lot quieter now. If you haven't tried this yet you can spray carb cleaner around the base of the supercharger and LIM, vacuum lines, etc. It can help to locate a vacuum leak. Also, spray your upper and lower EGR tube, they will develop cracks that can be very hard to detect. The scan tool is probably the most useful item in my tool box though. Is your check engine light on?

Thanks I'll check into the scanner. No engine light on, I have one code stored 58 for VATS problem thats it. I did have a code for the PCM that is why I replaced it as well.

I'm thinking that it could either by a vacuum leak that I haven't been able to spot, a bad EGR, or bad injector. My shop manual says to test fuel injector balance by monitoring fuel pressure and firing one injector at a time. Unfortunately I think I need a special tool to individually fire the injectors. Do you know how to do this? I was thinking about unplugging all injectors but one and turning the engine over to check.

Oh and I have sprayed all over with carb cleaner looking for vaccuum leaks, haven't found any yet. I bought a vacuum gauge as well, but it hasn't told me much. Pretty much just holds steady vacuum at idle..

No, I don't know how to fire the injectors seperately. I think you have to have the Tech I that the dealers use.

Ok thanks.

Just reading up on the CP9145 - I think I need to get one of these bad boys

You may have already checked but a leaking diaphram on the fuel pressure regulator will cause rough idle. You check for leaking gas at the vacuum fitting.
I had engine missing and the shutter at 45mph (Torque convertor lock in speed). Went through all that stuff you listed and discovered from the forum that you should NOT use platinum plugs. Got the inexpensive copper ones and no more issues. Good luck

Yeah I did check the pressure regulator vacuum hose for fuel, didn't see anything leaking there. Thanks for the suggestion though.

As far as the plugs, yeah I just use the regular copper ones.

I did find that one of the hoses had popped off from the charcoal canister, fixed that but she is still running rough.

Chantspel, I posted earlier to use carb cleaner to check for vacuum leaks. I have since learned that carb cleaner leaves an oily residue. I have a pool sitting on my intake manifold now. If it were to get sucked into the MAF sensor for example it could cause problems. So I will be only using MAF cleaner to check for leaks from now on. Also, does your rough idle occur mostly below 1500 rpm or above. Is it more of a cutout, stumble, surge. The reason I ask is I have the FSM'* for the 95 Bonneville and I am spending the weekend reading instead of chasing ghosts. If we work together on this we may be able to learn something and save a little time, money in the process.