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1995 Grand Prix GTP 3.4 DOHC rough idle and miss.

6

67GTO

New member
I just started to get a rough idle and a miss while driving. It seems to have started after getting gas but I am not sure it started then. It has the rough idle at start up and when the car is warmed up. I also don't get a check engine light. Any ideas where to start looking.
 
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Re: 1995 Grand Prix GTP 3.4 DOHC mounts rough idle and miss.

When was the last tune-up done? Could just need fuel filter, plugs/wires. Might also want to clean the MAF.
 
Re: 1995 Grand Prix GTP 3.4 DOHC mounts rough idle and miss.

The possibilities are many.

Most likely
Plugs
Plug wires
Ignition coils (3)
Fuel injector(s)

Fairly common
Ignition control module
Fuel pump
Fuel filter
Fuel pressure regulator

Less common
Head gasket
Vacuum leak
MAF sensor

Any of the above can be a problem without triggering a code. I would start with the easiest, and work your way down. If plugs, wires and the fuel filter haven't been done in a while, it can't hurt to replace them regardless. Not expensive to do. They're a bit of a pain to get to, but you can remove the coils and ICM to have tested for free at most parts places if you don't have the means to test them on the car. Fuel pressure can be checked with a gauge to see if the pump or regulator are failing. The biggest pain is going to be getting to the injectors to test them. Here's a good checklist to try to diagnose a miss. http://troubleshootmyvehicle.com/gm/3.8L/troubleshooting-misfire-codes-1 It's for the 3800, but the principals are the same for most motors.
 
Re: 1995 Grand Prix GTP 3.4 DOHC mounts rough idle and miss.

The car hasn't been tuned up since I bought it 3 years ago. I paid $1500 for it and just use it to go to the train station. It's a good car and really haven't had any problems with it. I have to do the inside mount(another thread) and find out what this problem is. The inspection is due the end of September, it is just a safety so I have to get the mount done. I worked as a mechanic for about 15 years and have worked on cars for over 40 years and don't look forward working on the engine.

I added some injector cleaner yesterday and will clean the MAF today. I have to wait until I get a few days off to check the rest of the stuff out.
 
When is the last time your timing belt was done? It could be easy over due. Pop the timing cover inpection cover off and see how it looks..it could be slipping and you might have jumped time....but I would check the obvious first plugs and wires...good luck getting to the rears...also the 95 gp is obd 1.5 so it may not read misfires as good as obd2...and that mount is a #$@/&

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76000 miles and the belt was never done as far as I know. I am going to let the gas I have in the tank now run low and then put some new gas into it. It seemed to start to act up after getting gas. After that I will start to diagnose the problem.
 
Belt supposed to be done at 60k so you are already overdue and the age of the car is not helping the belt. I would pop the cam cover off really quick (2 8mm bolts) and see if it is falling apart...regaurdless it needs to be done then you can change all your plugs and lim gaskets if you plan on keeping the car.

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timboku said:
Belt supposed to be done at 60k so you are already overdue and the age of the car is not helping the belt. I would pop the cam cover off really quick (2 8mm bolts) and see if it is falling apart...regaurdless it needs to be done then you can change all your plugs and lim gaskets if you plan on keeping the car.

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I actually checked the belt at the beginning of the spring and it looked fine. The timing belt isn't getting changed at this time. If I plan on keeping the car it will get done next summer. I payed around $1500 for the car and my wife uses it to go to the train station and I use it in the winter to go to work. I have the car 3 years and put 6000 miles on it.
I am on vacation next week and will try to change the plugs and wires.
 
i had a 96 3.4 DOHC would do Tbelt every 80k. the issue that killed the motor was that there is a timing chain the drives the timing belt... 225,000 miles and the chain tensioner went and caused the chain to jump time. belt was still great. was a perfect time to swap to a 3.8.

these engines are know for vac leaks. if you havent done them, and plan to keep the car do your lower intake and upper intake gasket set. it also will make doing the plugs easier. also the icm is under the front exhaust manifold and can have issues. i would relocate it. the 96+ had the coils on top of the engine for this reason.
 
Started to check it out yesterday. Used a test light to find out the cylinder that had the miss. I was lucky it was #2 cylinder. Took the wire off and used a plug I had laying around and attached it to the wire. I started the car and the plug had spark. Well either it was the plug or the injector that was bad. I didn't want to pull the plug because the engine was still hot. I originally thought it was some bad gas so I drove the car until it was on empty, put in gas and then put in some Sea Foam injector cleaner. Took the ca on the parkway and sure enough the car started to run better. I drove it around for the rest of the day and it now runs like normal and idles smooth. So one problem solved for now. I am off tomorrow and will tackle the mount and power steering hose leak.
Thanks to all with help and suggestions.
 


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