95 SE erratic idle, hard starting, stalls, no Check engine - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 08-19-2007, 04:49 PM   #1
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Default 95 SE erratic idle, hard starting, stalls, no Check engine

I am a new member, but have read many posts. My dad has 2 Bonnevilles. Now I have one.

A friend gave me a 95 bonneville se w/135K miles. Had telltale signs of UIM failure, and was stalling on him, hydro-locked up once on him (i think) but turned over when he had it towed to me. He gave it to me, and I figured I could fix it for cheap and sell it. He was cool with that, and just wanted to know what the problem was.

I replaced bad UIM with new unit per Juniors 3800 tech page, and also replaced LIM gaskets with GM aluminum frame units(PN was one digit different than web page) (the orig plastic ones fell straight apart). Coolant was everywhere, but I took car to get it all out and pulled plugs and cleaned them, got all cylinders dry. Oil looked free of coolant. Perhaps errantly, I disassembled TB of sensors, and cleaned it all out, since there was a bit of coolant in there. MAF wires looked okay, I did not rub or touch them. Everything went back together easily enough.

Initially, car would not start - had spark, etc, but it didn't want to hit. I tried over several days. Finally, days later, after re-checking everything, it did just fire up. I did nothing to cause it to start. It spewed vaporized coolant out exhaust. Shut her down and restarted a few days later, and vaporized all coolant in the exhaust system - took about 5 minutes. I needed to work the gas initially to to keep it running, but then it settled down. Idle RPM seemed high at about 1000 to 1300. Never had any check engine light. I do not know if there are stored codes or not.

FFW to today.
I thought I was in the clear, and tried to start it to go and get my Virginia (Leesburg) state inspection, and had starting problems. Initially it would fire, and then immediately die. Did that about 20 times. Eventually it started, and I was able to get 1300 RPM idle. It would regularly miss, but recover. Put AC on, and it seemed a little better. Finally got it warmed up, and it idled at about 1100RPM. Took it for a drive, and stalled on me 5 times, especially coming to a stop. Had nice, strong power above 3000RPM, though.
It did still have a couple very intermittant miss events. I have basic tools and a multimeter - so I can do basic diags. Battery ground is good. No known interior electrical issues, but I have not checked chassis ground yet. Vacuum is good (i did replace a couple hose pieces)

So, so far I have spent $105 UIM $70 LIM gaskets, $15 oil and coolant, $100 to $120 VA tags. $10 Wiper blades. It needs to idle to sell it. My wife wants it towed away ASAP. I am hesitant to throw sensors or other parts at it without a good chance for success. I figure car is worth $1500 to $2500 if it would run and start better. Since 95s have ODB1.5 I am hesitant to take it anywhere but a GM dealer, but I know they might charge my $$ which might make the whole project not worth my time and effort. I do not have a manual.

My current thoughts are PCM, MAF, crank (or is it camshaft) position sensor , based on other posts I have read. Any thoughts? Alternatively, anyone want a 95 Bonne Se with a new UIM? I've got one for the cost of my parts + $250 for new sway bars for my Cosworth Vega!

Any help is appreciated! Thanks,

Ken
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Old 08-19-2007, 06:39 PM   #2
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Did you replace the spark plugs? Coolant can ruin them.
Make sure the wires are going to the correct cylinders/coils.
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Old 08-19-2007, 06:50 PM   #3
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Yes, all wires are correct. Once it starts running, it really purrs, and except for the occasional stutter, it is very smooth running. Wires are correct. I checked the plugs, and they looked fine, and I cleaned them, and re-gapped them. They were all close.

More tests done today. all coil packs primary and secondary windings matched and were within willwren'* limits. IAT sensor OHMS seemed correct. Blowing (my hot air ) through the sensor changed the ohm readings acceptably. I was going to check the CTS, but it is a 3 wire sensor, and I was not sure how to test it.

I'm thinking maybe a Camshaft position sensor now.....but still searching through old posts.

Ken
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Old 08-21-2007, 11:12 AM   #4
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More questions...

1) Anyone know how to test the 3 pin CTS?

2) does the water pump belt or pulley have to come off to replace the CPS? what about to look at the camshaft magnetic trigger? can I use a mirror?

3) WOuld DTCs be stored even if I don't have a check engine light on? is it worth it to take it to a GM dealer to do a diag on it?

Ken
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Old 08-21-2007, 11:35 AM   #5
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First thing I see here is a good possibility of a vacuum leak.

Check the plug in from the brake booster behind the upper. Also check the other connection right on that same piece and that the tube connects to the vacuum canister at the firewall. Then check the TB side of things and ensure you got it all hooked back up w/o any leaks. This honestly sounds like a large vacuum leak.
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Old 08-21-2007, 01:05 PM   #6
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I agree with Bill that this smacks of a vacuum leak to me. Another possibility, since you've just done the UIM and LIM gasket replacement, is the EGR tube under the TB. More than one person here has had vacuum grief from that little item not being seated correctly or from a crack in that tube.
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Old 08-21-2007, 01:59 PM   #7
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So the theory here is vacuum leak increases engine idle speed?

I was wondering about vacuum leaks. I did re-check all the hoses, and they seemed good. The brake booster fitting into the manifold seemed loose to me, though. I will check it again. Should I get a can of ether or the like and spray by that fitting to see if it increases engine speed? I was gentle with the EGR pipe, but I did have to take it all the way off, because coolant had gotten inside it. I will make sure it is re-seated and not cracked.
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Old 08-21-2007, 02:45 PM   #8
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Use TB cleaner or carb cleaner for your testing. Ether is too flammable and dangerous to use on a running motor. You may blow your composite intake to shreds.
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Old 08-21-2007, 10:17 PM   #9
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Quote:
Originally Posted by lash
I agree with Bill that this smacks of a vacuum leak to me. Another possibility, since you've just done the UIM and LIM gasket replacement, is the EGR tube under the TB. More than one person here has had vacuum grief from that little item not being seated correctly or from a crack in that tube.
You mean it seats? Where and how? It seemed to just flop around in that larger-than-the-pipe hole. Is it supposed to seat in that egg-shaped black plastic cover that it goes through and is bolted to the LIM with a single bolt? I haven't managed to locate these details in the FSM yet.
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Old 08-21-2007, 10:33 PM   #10
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A measure of success! Cheers to Bill. It seems that a picture is worth a thousand words.
Name:  95L36PCV.jpg
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The old owner had a new PCV valve in the glove box, so I just installed that one - but it did not come with an o-ring. I did not realize there was an o-ring stuck in the old manifold. I had never seen this design before, and assumed it just dropped right in. After inspecting it this evening, I realized there was more play around the PCV valve than I thought. I found a sutable o-ring, re-installed, and seem to have markedly different (better) performnace tonight!

I am not sure I am quite there, though...

The car started right up. Idle dropped from 1300 to 900-950 RPM, over the course of 2 minutes. Idle smoothed out, and the regular miss went away. I drove it and did not have any stalls. I parked it, and turned on the AC, and after about 10 to 20 seconds it stalled. I restarted it and it ran fine. turned on AC again, it stalled. Started it and tried a third time, and it kept running this time. The car still tried to maintain 950 RPM. A couple of times, as the idle tried to creep lower, it stumbled breifly and went back to 950 to 1000 RPM.

Other notes: Oil pressure was 24psi at idle. I forgot to look when I was driving. Temperature did not want to go far above 200deg on gauge, but when it did, The fans kicked on, as they did when I turned on the AC. I think the CTS is working. Ambient temp was 65 to 70deg, high humidity.

I was worried exhaust manifolds got too hot for me to try to check for other vacuum leaks tonight with carb cleaner, but brake booster fitting did not seem to be leaking, nor did any front vacuum connections. No vacuum or draw from the oil cap, and no engine speed change when I removed it.

Am I good to go? Should I try a couple of other things? I hope to get a state inspec tomorrow, so long as it fires up in the morning.

Thanks, Ken
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