^ cyl. pontiac grand am.. running very rough


Asked by Dec 11, 2010 at 08:08 PM about the 1999 Pontiac Grand Am 2 Dr GT Coupe

Question type: Maintenance & Repair

My girl's car suddenly started to run like it was only firing on half the cylinders yesterday, I bought new plugs and changed them thinking she may have fouled a couple for some reason.. The old ones were in pretty bad shape.. This did'nt help so I checked all the wires one by one hooking a plug to them and starting the car to check each one for spark. all were good. Been around enough cars in My time to know that if You have fire, You should get some kick from the engine.. Wondering about the o2 sensor or possibly a bad fuel filter. Thought at first maybe even some bad gas but She drove out a half tank of what was in there before it started to run like this..And also it's not a rod knock or about the oil, just feels like a dead cylinder or something.. any thoughts?

26 Answers


Mass Air Flow sensor, had the same problem with a Bonneville 3800. Could also be the coil pack.

5 out of 5 people think this is helpful.

check for vac leaks,bad cam sensor,if it has a bad 02 sensor it would through a ses light.

2 out of 2 people think this is helpful.

As you give it gas does it run better? Also is it throwing anying codes/Check engine light on?

23 out of 23 people think this is helpful.

Giving it gas does'nt help.. When it first happened for Her She did gun the car and it ran better till She got Home. Once in the driveway, it started to run really rough again and I havent been able to gun it to blow out the cobwebs so to speak...

10 out of 10 people think this is helpful.

is it 4 cyl or 6 cyl,if 4 what kind of spark plugs are in it,the 4 cyl onley likes the orig gm ac delco plugs,it wont run worth nothing withany other plugs,also if 4 cyl replace the boot covers for the plugs.

3 out of 3 people think this is helpful.

try taking the towwer cover off (qaud 4 engine)and using a test set of plug wires to connect from the coils to the plugs , reconnect the module and do a manual cylinder balance, you might have a bad ignition coil or a cracked coil towwer housing, most likly a bad coil .

3 out of 3 people think this is helpful.

Checked the coil pack. Even bought a new one and worked it through all 3 seats. Bad news got worse when I was checking them, the engine acted like it seized up. was actually running at a slow idol when it happened (car was about to stall). This DID NOT sound like the typical rod knock...My only hope is that this engine's timing belt jumped a few teeth and eventually let go completly causing extreem vapor lock, or an intake valve got caught open on a pistons tdc. Have to wait for the weather to clear to tow it to My garage tho.. (no fun working in a snowstorm).


When you took the spark plugs out what did they look like? fouled with carbon/burned. Or were they like chewed up with holes/ piece missing from them?

1 out of 1 people think this is helpful.

The plugs were worn down like they were just old. none of em were even fouled out. That's why i'm starting to look at the whole timing belt issue...

1 out of 1 people think this is helpful.

what engine does this car have? A Quad 4 engine dosent have a timing belt. Its a chain driven motor and on high mileage Quad 4's its common for the chain to become loose as the spockets wear, also timming chain tensioners are very common too. Is this a 3.1 V-6 ? do you have any codes ? is the check engine lamp on ?

3 out of 3 people think this is helpful.

You might be better off getting it daignosed from a shop and be done with you headache.

is it a rough idle or running down the road smooth or rough,does it idle rough at stop lights then run fine,if so you got a bad tranny mount,their is 3 of them,

9 out of 9 people think this is helpful.

do all the fuel injectors work? I've had a bad harness, broken wire, cause it to feel like my v-6 was running on 5 cyl.


It's a 3.4 litre engine so not sure about the belt vrs. chain issue.. Yeah, no codes since the engine wont run at all now.

1 out of 1 people think this is helpful.

I re-read your first post and you said it started to run bad when you were at half a tank. Would be curious to see what you fuel pressure would be at idle, and after a few minutes sitting off. The fuel pressure spec for running is between 41-47psi, and should drop more then 5psi after sitting 10mins.

4 out of 4 people think this is helpful.

Was starting to lean torward the the fuel pressure being bad for what ever reason i.e. pump, bad filter. But now that the engine seem's to have seized up, I'm going to have to look into weather or not I lost the timing belt while I was trying to figure out what was going on with the car. When the engine was actually running, it was turning over like the timing was advanced way too far as I tried to start it up... It's a 3400 so Im not actually sure weather it has a timing belt, or chain ...

2 out of 2 people think this is helpful.


1 out of 1 people think this is helpful.

If its the 3.4 liter engine check the rocker arm studs. General Motors changed from a 10 mm stud To a 8 mm stud and the strip out the threads in the head if over revved. I have had 3 studs pull out in 40000 miles You have to retap and install a helicoil in the head. Just cost meme 650 bucks to have 2 redone and all others checked.

4 out of 4 people think this is helpful.

I have a 96 grand am i bought an engine for it but it was a 4 cly and my car is a 6 cly. Will it matter?


If the oxygen senser wires get pulled off of the cat.. wood this cause my 02 2.2 garand am to just stop running? I replaced fuel pump thinking it was not getting fuel from tank an I replaced fuel filter. When car still ran I was about an hour from home fishing. Started car to come home it drove aproxmently a city block an thin cut out realy bad and nearly wonted to go with a lilbit of shimmy an then died. About 4 min later it half jazz started up an I floored it an it seemed to unbog its self and got me a block from house and died an will not start just wine an turn..also rewired them wires during break dwn. if you know what it could please let me know

4 out of 4 people think this is helpful.

I had the same issue....a new Ignition Module was the fix. I had it fixed 20,000 km ago by the dealership under warranty (58,000 km on the car at the time). I know have 78,000 km and it went again. Except this time...my extended warranty expired the day before it blew. Hoping I get them to fix it this time.

3 out of 3 people think this is helpful.

My car felt like it was going to stall when sitting at a red light so I would put it in park and it would idle ok. As soon as it was in gear, the hitching would continue without having gas pedal pressed. Limped it to the dealership. I only drove about 8 km each time straight to the dealership.

11 out of 11 people think this is helpful.

Oh - I have a 2008 Grand Prix 6 cylinder, 3.6L.

2 out of 2 people think this is helpful.

2.5 liter 4 - cyl, air idle valve, replace! don't bother to repair, i tried no good! Also: the coil pack module behind the engine is susceptible to heat! Remove, it and extend wiring harness, and plug wires to cooler location. These nice cars are getting OLDer -- TLC is required to keep them running... not expensive repairs, that don't last....

3 out of 3 people think this is helpful.

Hole in a hose or lose vacuum line. It also affects the shifting and the brakes, ( occasionally). Check for cracks and holes and check to be sure nothing that sucks is plugged up. ( manifold)

2 out of 2 people think this is helpful.

If ya have a problem finding a leak in a hose find a kid on your block that , so called "tunes", and have him smoke check your hoses for a couple of bucks. They know how, and it would take forever to describe the process. This is a sure way to find out if its a leak.

1 out of 1 people think this is helpful.

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