1995 Bonneville: Bad idle, stalling, shaking, backfire

[Twystedhemp2]

This problem started over a week ago right in the middle of a road trip. It began while going uphill on cruise control at 65, it started choking and sputtering, took off cruise, gave it gas and it stopped. At the next stop the check engine light came on. Now it cranks right up but won't idle, IAC was making lots of clicking noises so we went ahead and replaced it. It ran good that evening but started again with the bad idle the next morning. Had the battery checked, tested bad so replaced it too. No improvement. Went over all air hoses, patched and replaced anything that seemed even slightly suspect. No improvement. Now not only is the idle bad, it also stalls out. Mostly at idle but it's also cut off under acceleration a few times. There is no parts shop in this town that can scan codes from it so I don't want to keep throwing money at sensors. We have a diagnostic scheduled for later in the week at a dealership but if there is anything we can keep testing that would be better on the finances. This is the first time we have not been able to pin down the problem in the four years we've had it. Fuel pressure regulator is spraying when tested but don't have the tool to check pressure. No, have not checked plugs, what are we looking for when we do. Battery and alternator check out strong but there is a drop in the dash board battery meter as it begins to stall. Checked and cleaned connections. The belt tensioner had to be replaced two years ago, could it failing again cause this? How can we check tension accurately? It looks and feels the same as it always has. Any advice would be greatly appreciated, thank you!

[Twystedhemp2]

Oh, also replaced air and fuel filters. Replaced all relevant fuses under the dash, both sides. Coils replaced two years ago. 216k miles, 90% highway, know all previous owners.

[J Wikoff]

Does it behave different when the maf is unplugged?

[96 SSEi]

unplug the maf sensor on top of throttlebody - near iac

[Oldman]

I can't understand how you can be purchasing all the parts, and have no way to scan for codes. I thought every parts store provided this service.

[Twystedhemp2]

The 95 has an OBD 1.5 scan system. That is why it is scheduled for a dealer diagnostic, no parts store in this town has one. I will try unplugging the MAF and let you know how it behaves.

[Twystedhemp2]

Dealer came back with a diagnosis of crankshaft position sensor. That sound right to you?

[J Wikoff]

Sounds possible. Did you get the code number?

[Twystedhemp2]

No, they were not exactly over helpful. They put the plastic engine cover on wrong... The oil filler cap was screwed on crooked...The engine was smoking hot like they hot-rodded it up and down the interstate or something, I can't stand letting people work on it out of my sight, something always ends up messed up.

[redfury]

A bad crank sensor could be the problem, but check the wiring leading down to it first. These were known to have exposed wiring due to oil leaks traveling down the wiring and breaking the insulation down. Replacing the wiring is easier than doing the crank sensor ( I've done it recently ), though the crank sensor isn't terrible if you have the harmonic balancer puller ( Which you need ), as well as a good impact or are comfortable breaking the crankshaft nut by cranking the engine over ( there's a video on how to do it )

[AJT2004]

For whatever it's worth, when I experienced a similar problem it was the ICM. Although it tested OK, it malfunctioned when it got hot.
Also, how are the spark plug wires?

[J Wikoff]

Thinking back, I've had a crank sensor go bad before. It got worse with heat and acted kinda similar.

[Twystedhemp2]

There were indeed open wires going back under there belt area but after patching them it is acting crazier than ever. Revs up and down at idle and still stalls at idle or while driving. The sensor seems like a bit of a hassle to get at. So the puller is a must?

[MattStrike]

Yes, puller is a must. Also, the kit's in the auto stores don't come with the correct threaded bolts, I believe there's another kit that has the bolts, I can't recall what thread they were but it's either M6 or 1/4-28 (fine thread). Make sure you use the right ones, as they are a close fit between the M6 and the 1/4-28 and running the wrong ones in will damage the threads on the balancer.

The hardest part is getting the bolt off. What I do is put a 6 foot pipe on the end of my breaker bar, and run a screwdriver along the oil pan and into one of the holes in the flex plate to hold the crank from spinning when breaking the bolt loose. Don't try to pry on the edge of the trans and a tooth on the flexplate, it will crack the trans case. I've never been able to crack that bolt loose with the starter motor method.

Also, there is a plastic cover behind the balancer that is held on by snaps. Don't throw it away, it keeps the wire for the cam sensor from hitting the balancer.

On the wiring, do you have access to the diagram for the harness between the ICM and the crank/cam sensors, and a DMM or something similar? It's possible that some of the wires you repaired got mixed up too.

[Twystedhemp2]

I had to get someone to do that crankshaft sensor...not the problem. What a crappy dealership. Not the ignition controls module either... Found a mechanic though with a fancy diagnostic machine, it is showing something in the MAF circuit. Took out the throttle body and cleaned it, that helped alot! Now it only stalls at idle and not as often, so we have the MAF sensor and EGR valve on the way and hope one of those finally get it running right. The mechanic also thinks the diaphragm in the brake booster may have blown from the fluid leak, that could cause some of this mess too right? He checked our fuel pressure too and it checked out alright, so did the injectors. Almost fixed!!! :D

[ron350]

Can you elaborate on what fluid leak could have caused the brake vacuum booster to go bad?

[Twystedhemp2]

Brake fluid leaking from the master cylinder.

[ron350]

Brake fluid wont hurt any rubber part inside of a brake booster but brake fluid will eat up your paint.

All rubber parts in a brake vacuum booster are made out of Ethylene Propylene the same rubber used in the master cylinder. All of the brake parts that can come in contact with brake fluid are made out of EP to make sure a brake fluid leak wont damage the rubber. That is why you have to use special grease on the brake caliper slide pin boots.
Ethylene Propylene and natural rubber are the only affordable rubber materials that will work in brake fluid but they don’t like solvents or oils.

PS; Don’t forget to check your egr corrugated pipe for cracks that will cause a vacuum leak..

[Twystedhemp2]

Oh, hmmm. Thanks, will check the egr pipes closer. So could the diaphragm in the booster be bad from just age? Pretty sure it's the factory part. When we can get the car to idle and press the brakes there is a small change in rpm so we thought this could be the strange something we have been missing.

[96 SSEi]

no, the booster works on vacuum.
unplug the maf and see if idle returns to normal