Car is misfiring and idling high

JUSTINT3771

MEMBER
2001 PONTIAC BONNEVILLE
125,000 MILES

Hello. I am finishing the list of maintenance items on my car. I was on the last two things oxygen sensor and throttle body/MAF clean. I did the oxgen sensor and I gained 5 MPG everything went well. Then I took apart the MAF and throttle body and cleaned them with the appropriate things.

Here is where the problem is, I got a new gasket and put everything back together and started the car. It idled very high at 1500 RPM for a couple of seconds then dropped to a constant 1000 RPM and the engine began to shake wildly.

I double checked that everything was re-installed properly and found that the throttle cable had a little bit too much slack but adjusted it and I think it's back to normal. So I retried it and ended up getting even worse engine performance and a misfire code for cylinder #6. I checked all plugs, wires, and coils and they all checked out alright.

I am currently stumped and don't know what I could have done wrong in cleaning the throttle body and MAF sensor but now i'm stuck with a car that vibrates like crazy, and would appreciate any help I can get.

4 Replies

HMAC300

MECHANIC
48,601 POSTS

Check to see if he maf is plugged in correctly and air ducts are hooked up, you may have an air leak between air cleaner and throttle body. Did yo clean iac hole and plate on both sides?

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Wednesday, May 29th, 2013 AT 6:38 AM

JUSTINT3771

MEMBER
3 POSTS

I just double checked but all of the sensors that I unplugged are plugged back in correctly. MAF, IAT, IACV. I took the throttle body off and cleaned every part of it meticulously. I also just checked everywhere for possible air leaks and can't find any before or after the MAF, which is why i'm so confused.

Is there any component that might be damaged or some other area that could cause misfiring and an improper air/fuel mixture? Thanks in advance.

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Wednesday, May 29th, 2013 AT 8:24 AM

HMAC300

MECHANIC
48,601 POSTS

This really needs to have a pro type scanner hooked to it and read as well as a fuel pressure check. Something can be amiss that just won't show up on store bought scanners. That way it will pick up what is bad. Also check for a vacuum leak maybe at the throttle body where pcv valve h ooks up it may beleaking vacuum and causing the shaking. Other than that I cannot think of anything else.

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Wednesday, May 29th, 2013 AT 8:35 AM

JUSTINT3771

MEMBER
3 POSTS

Hi, thanks for your help so far. I re-evaluated the vacuum hoses and found a small rip on one, I went to an auto parts store and they were able to fabricate a temporary replacement until the one I ordered from GM gets here. It was a small vacuum hose attached to the throttle body, I'm guessing fuel evaporation line or something of the sort.

Anyway, after driving to the store and arriving back home I noticed it wasn't shaking or surging anymore, but there was still a tick and occasional misfire.

I think this is a past problem I had coming up, either my valves are dying or something else because I just replaced all spark plugs, wires, and coils a few weeks ago.
I'm going to add lucas fuel stabilizer and seafoam through a vacuum hose and take it for a drive to see if that cleans out any remaining gunk.

Thanks for the help, is there any other thing that may be causing a misfire besides my plugs, wires, and coil? There is a slight ticking but I can't tell if it is an injector or the valves, or something completely different thanks.

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Wednesday, May 29th, 2013 AT 10:02 AM