kman522

Engine Performance problem
2001 Chevy Cavalier 4 cyl Front Wheel Drive Automatic 106000 miles

Guys hopefully you can help me. I have a 2001 Cavalier 2.4L. I recently had the water pump replaced due to it leaking and now after I picked it up from the repair shop it idles worth a darn. I never had this problem before. Idles very rough almost like it is running on 3 cylinders. When I drive it down the road it seems fine. I have checked for vacuum leaks and found nothing. I even sprayed the area with carb cleaner while running to try to detect the hidden vacuum leaks and still nothing. I changed the plugs which seemed to help a little but not fix the problem. I dont think my car is equipped with a EGR valve? Everything I read points to this but I am thinking my car doesnt have one? I checked the IAC motor and it moves in/out when the key is turned.

I have no codes on. I also cleaned the throttle body which was dirty still rough idle and hesitation once I start moving. I am at my wits end with this thing. Found out my car has no EGR valve nor does it have a mass air flow meter.

One important question: If my timing was off when the water pump was changed, would I notice it? It seems to run fine at road speed just idling is my issue.

HELP

cive666

I don't think its a mechanical timing issue. Yes, the water pump is ran off of the timing chain. but when it is serviced it is just simply slipped out of the chain housing; the timing chain and gears on the cams and crank do not have to be moved. It would have to be very deliberate to mess up the mechanical timing on this engine when changing a water pump.

From what I read here and on your link where you had some trouble shooting, I would agree it is running rich, that smell is always a dead give away. The throttle surging is probably from your computer seeing a rich state and it attempting to correct it by leaning it out making you idle go up, then starting all over. I would expect to see you STFT (short term fuel trims) to go way negative to try to correct this, then bounce back to a positive number.

I would look for a possible leaking injector, fuel pressure problem or a spark plug not firing.

On this engine checking the spark plugs for firing is kind of a pain. What I do on engines that you have easy access to the wires is just connect an inductive pick up amp gauge to see if there is spark. On this engine I would get some spark plug wire that are long and unbolt the coil housing set it aside and connect the wires and check that way. Some may do it a different way, if anyone can suggest an easier way. I would just go to the junk yard and get some wires from a 2.2 engine, they should work.

Leaking injectors have to be flow tested, most shops are capable of doing this. You could check for a leak you self by taking the intake off and re securing the fuel rail and pressurizing the system and watching for leaks, but just loosing the fuel rail and unplugging the injectors to take somewhere and paying to get them check would be A LOT (stressed) easier.

I hope this helps, pease update if anything is found.

kman522

Thanks for the reply. I like your idea of checking the plugs. There are a couple of spark packs that run the 4 cylinders & I changed the plugs so I think they are ok. I would suspect that if I had a bad spark pack I would have 2 cylinders not firing? Your thoughts? Maybe I am wrong?

Unfortunately I am out of town for the next few days & am looking at dropping off my car to a different mechanic this Friday. After talking to him he thinks timing? I prefer not to drive it like it is since I have a hard time keeping it idling in traffic.

Just find it a little suspicious that if it is an injector it going out when I have some service work done to it. I am not trying to bash my 1st mechanic. I am 100% sure nothing intential was done. Just need to get it working.

Once again, thanks for the help.

cive666

You are right about the coils, they fire at the same time for 2 cylinders. The 2 things that control ignition and injector timing are the crank sensor (spark) and Cam sensor (injectors). I still can't believe that it would be mechanical timing.

I wonder if this new water pump caused a weakened head gasket to start leaking.

kman522

After bringing it to a recommended mechanic, he discovered the timing was off by 3 teeth (retarded) causing the rough idle and lower power. $80 later I have now a new mechanic and a well running car.

cive666

wow, I can't believe that your first mechanic caused that issue. It is a good thing your valves were not bent from this.