Engine sputtering, rough idle, cuts out under power

HELP!

My wife's car is a '95 Monte Carlo LS 3.1L V6, automatic, power everything, onyx black with graphite leather interior, 16" rims, multiport fuel injection. The car has 88,000 miles and we are the second owners from the 13,000 mile mark on. It has run great in the past, and the only things I've had to fix on it were a cracked manifold in 1998 (under warranty) at 30k, KYB gas struts at 36K, tires at 32K and again at 86K, serpentine belt at 65K, and a battery at 80K. I've done tune ups at 40K, and 80K, and regular oil and air filter changes using synthetic oil. She is in another state right now, and we are trying to get her home. If figures it would happen like this, because it removes me from being able to do the work I could normally do without getting gouged by a garage. Her car started cutting out on her under acceleration at speeds over 55mph about a week ago, so I thought she had a plugged fuel filter. I had a friend change it for her, and it ran fine for a day, and now she says it is cutting out again, only now, it runs rough at idle at a stoplight, and she has to give it a little gas to keep it running. It doesn't happen at any particular temperature, morning, afternoon, or evening, it is intermittent. Sometimes she'll go out start it up, and it'll run fine for a few miles, other times it'll start up and run crappy, then run fine after a few miles. The check engine light has never come on, and my buddy that changed the fuel filter ran it on a scanner without any error codes coming up. Any ideas, we're trying to get her back on the road, but I want to have a sure fix, as she'll be travelling 1600 miles in the car, and I don't want her having any other problems. Thanks for the help. CReM

 

If the O2 sensor has never been changed, that will be one possibility. Hopefully Joe, (aka G.M. Joe) will be along with additional ideas.

 

Check the fuel pressure with a reliable hand held gauge.....it seems it might be fuel related (changing the fuel filter seemed to help). Autozone or any retailer with a tool rental program can provide one.

Check www.autolibrary.org with the spec. Let's start there.

 

Thanks guys for the replies. I hadn't thought of the O2 sensor, is there some way to test it before buying a new one? Nothing showed up on the scanner indicating it was bad though. I asked if they had checked the fuel pressure, my friend said he did it after changing the fuel filter and the pressure was up, and remained steady without fluxuation. He said he made sure to do that because his experience is that after changing fuel filters on high mileage cars, that sometimes he's had the pumps go out a week or two later. What is the consensus on bad gas. My wife said that she filled up the day before the problems started, and the next day it started cutting out. She filled up with premium yesterday and said that it seemed okay. I wonder if this is an intermittent episode again? I told her to get a bottle or two of HEET and put in the tank. She also said she was driving last night when it was cool, not in the heat of the day. How would temperature affect things? Thanks again, it's getting close to take off for her and I just want her to be safe while travelling. CReM.

 

Oh, I also forgot to ask, how do I test the Throttle Position Sensor? I know how to test the MAF sensor, tap it with a screwdriver or socket extension over the top while idling, but I've heard there are ways to test the TPS, and that it may be bad but not be registering a code. Is that true, and how would I test it? Thanks, CReM.

 

Should pitch the Monte Carlo and give her one of your better cars in the fleet to drive . I hate those front wheel drive W body cars....they aren't very good .


It could be vapor lock. Have you checked www.alldata.com for known bulletins that might match the problem at hand?

 

Well, I would, except all of those cars have been moved to TN, and she is still in UT. I agree, the '67 Camaro made the trek 1600 miles with nary a hiccup, that's why I have them. Unfortunately, we were waiting until the move was over to sell the Monte. I'd like to see what the new Pontiac GTO will be like with the LS1. That way she gets a new car with warranty, and I get a rear drive V-8

 

The throttle position sensor is checked with a digital volt meter or a scanner to see for problems with the voltage being out of range or an erratic sweep on the meter across the range.

I doubt it is your problem.

Here's a thought....a possible sticking TCC solenoid (long shot, but quite possibly). Sometimes if the TCC solenoid sticks, the car will chuggle and act like a manual transmission when you forget to push the clutch in while decelerating. If this type of symptom is what you get, look for a sticky TCC solenoid. Unplug the connector at the top of the transmission and if the problem goes away, you've found your culprit.

Here are the bulletins and recalls on this vehicle. If any match your symptoms, see any GM dealer for the full printout to determine the fix:

http://www.alldata.com/TSB/951007_en.html

 

Okay, so my brother took the car and found a 4 prong plug and an 8 prong plug at the top of the bellhousing on the car. He unplugged the 4 prong plug, and then drove it. He said that the car was very sluggish from a start and took a while to get up to speed. Once he was up to speed on the freeway though, he had no problems with engine hesitation or cutting out. Does this sound like the TCC solenoid is bad, and how hard is it to fix? Do you have to pull the trans pan, or is it an unbolt and slide out item externally on the trans? Thanks, CReM.

 

Alright! So it looks like we've got the problem fixed. After taking the car for a drive with the trans plug undone, my brother decided he'd pull the plugs and check them just to double check things. When he got to the rear spark plugs, he noticed a vacuum hose laying down on the exhaust manifold, dangling. The end had cracked and broken off from some kind of sensor with two wire leads. He said one end of the hose looked like it went down to the transmission somewhere. Anyway, cut off the bad end of the hose, reconnected it and took it for a run. He said it had more power now than when he had driven it before without the cut out problems on acceleration. Thanks Joe F and the_tow_guy for the help, it looks like this is also why no codes showed up on the ECM. Man, somebody would have gouged my wife on this one if she had to take it in. Thanks again all, CReM.

 

That'll do it . Good job.