CEL and lower idle after timing belt change - HELP!

I've got an '03 P5 with 105,300 miles on it and took it in for a timing belt change per service manual. When I went to pick the car up I started it and reinstalled the car seat in the back, as I got in to drive away I noticed a CEL was on before even leaving the parking lot. Turned around and the guy scanned my codes and said I had a miss fire on Cyl #2. He thought it was probably because they removed the coil packs and everything when they did the service. He cleared the code and checked the connections on the coil packs and sent me on my way. I had also mentioned that the car seemed to be idling much lower then it usually did and running rougher. My car usually idled at about 900 and no it was maybe at running at about 700 and I could feel it. Before the service the car ran great, in fact I couldn't even tell it was running sometimes it ran so smooth. So to be sitting there be "feeling" the car seem like it's trying to stay running was a bit odd.

The CEL didn't come on the rest of the way home but it still seemed to be idling too slow and feel like it was fighting to keep the rpms up at idle, just about 700prm. Got home and unplugged both cable to the Battery and gave the car a wash and let it sit for about an hour before hooking the battery back up to reset the ECU thinking that might do it. Drove around today running errands, still seemed to be running rougher then it did and idle was still low to me at about 700 and not running great. Then tonight, leaving the drive way it threw another CEL light. I don't have scanner but I suspect it's the same misfire issue.

Would this be characteristic of my timing being off by a tooth maybe. It just ran so good before the service and no not so much. I did the service to keep it running good, not have it give me check engine lights every other day. If anyone has some insight they could share with me I'd appreciate it. Going back to the mechanic tomorrow so I hope I can show up armed with some knowledge of what the problem might be. Thanks

Take the car back and let the place that did the timing belt change sort it out.

MaxPower said:

Take the car back and let the place that did the timing belt change sort it out.

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+1, most likely they didn't get timing correct when they put it back together.

Ok that's what I was thinking since the car ran fine before taking it in. I'm just worried they're gonna tell me it's coils, plugs or wires and want another $200 in parts and labor to replace all of that stuff only to have the same problem remain. Wish me luck and hopefully they can get it all sorted out sooner rather then later.

Ride92 said:

The CEL didn't come on the rest of the way home but it still seemed to be idling too slow and feel like it was fighting to keep the rpms up at idle, just about 700prm.

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Your idle being at 700 is just about dead on. (although you obviously have some engine issues)




Remember too that our car idles like crap after the battery is disconnected while the ECU is relearning the car (although a misfire code shouldn't be part of that process)

Yeah I know that it's within range for the idle but it idles like crap, car feels like it's fighting to stay at idle speeds. Putting my hand the tailpipe I can defiantly feel a pulse that is not normal coming down the line. I still say the car is misfiring. Going to swap plugs this afternoon since it needs it anyway but I doubt that's the real problem. FYI I had both my coil packs changed at about 90,000 mi, car has 105,000 on it know. They shouldn't go bad that quick should they?

If I were you, I wouldn't do anything except drive the car straight back to the mechanic. There is a really good chance the T-Belt is off and an engine miss-fire is the worst code our car can throw,... it's the only code that flashes the CEL and can melt your pre-cat in minutes.

If you do anything to your car they may try to blame you for the problem and it's a lot of labor to get the covers off to check the timing so they won't be too eager to do it.

Your car may very well have another issue but they at least owe you a diagnosis to tell you what it is,... and you don't have to let them do the work or get the parts.


BTW,.. coils on our cars can be completely unpredictable and irrational. I was PM'ing a guy for two weeks with an engine miss-fire he couldn't figure out we went through the entire list and he even had a scope to help,... the engine would die as soon as he touched the probe to the ECU terminal ???,... It turned out to be the brand new coils he put on,... they would only miss-fire when the car had a complete heat soak.

They tend to wear out slowly and only miss-fire when they feel like it,... temperature, RPM, vibration, humidity, who knows. It's like trying to understand your girlfriend,... good luck asking her why she's giving you problems,...

This is the reason I work on my own cars. You know if you want to half ass your job and what you have to live with, the mechanic may not care as he still gets paid at the end of the day.

If working on cars is not for you, find a trusted mechanic and stick to him/her.

The_big_dill said:

This is the reason I work on my own cars. You know if you want to half ass your job and what you have to live with, the mechanic may not care as he still gets paid at the end of the day.

If working on cars is not for you, find a trusted mechanic and stick to him/her.

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Yeah, I hear on finding a trusted mechanic. I had one, for a very long time. My uncle owner and operated a small shop in my home town but he has retired so now I'm left searching for a new one, which sucks!

On the plus side, I got the timing belt thing figured out. Drove the car around for a day and got another check engine light and went thru a little over a 1/4 tank in less then 50mi. I changed the plugs just for good measure but that didn't help. Took the car back to the mechanic on Friday night and he found that the belt was in fact off by one tooth. He fixed it and now everything is running smooth as it was before!!!! Thanks for the help. At first he didn't want to believe that I knew it was off a tooth, knowledge is power and in the end I was right.

Ride92 said:

Yeah, I hear on finding a trusted mechanic. I had one, for a very long time. My uncle owner and operated a small shop in my home town but he has retired so now I'm left searching for a new one, which sucks!

On the plus side, I got the timing belt thing figured out. Drove the car around for a day and got another check engine light and went thru a little over a 1/4 tank in less then 50mi. I changed the plugs just for good measure but that didn't help. Took the car back to the mechanic on Friday night and he found that the belt was in fact off by one tooth. He fixed it and now everything is running smooth as it was before!!!! Thanks for the help. At first he didn't want to believe that I knew it was off a tooth, knowledge is power and in the end I was right.

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Glad you figured it out, and thank you for posting the solution, hopefully it will help someone else out.

Ride92 said:

On the plus side, I got the timing belt thing figured out.

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So what's your idle like now ??? Is it back to 900 or did it stay at 700 RPM ???

pcb said:

So what's your idle like now ??? Is it back to 900 or did it stay at 700 RPM ???

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It's right around 750-800 know but smooth as silk. I think the addition of new lugs helped get the idle back to where it should be. I'm now running NGK ZFR6F-11 long reach plugs which are one step colder then recommended ones for the car. In fact those plugs are the ones that come up as a replacement for the Mazdaspeed version, MSP, of our car. Must have something to do with the turbo setup on those cars. I'm not boosted but I was getting some bad pre-detonation under acceleration so I am hope that these colder plugs help that out a bit. If not then I might go back to the standard reach plugs just colder (6) instead of (5).

Ride92 said:

I think the addition of new lugs helped get the idle back to where it should be.

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I never thought new lug nuts would affect idle,... LOL