engine problem for REAL Gurus or Gearheads

[4SPEED]

03 GT
started out having P0304 codes and a miss at idle but could never feel it while driving. Intensity of miss would vary, engine temp and outside temp were not consistant. I started checking everyone's stories here and decided it might just be a vaccum leak at the #4 cylinder like others have had. So I dismantled it and found that none of the intake bolts were loose at all so I snugged them a bit more. I doubt that I had a blown gasket. Installed new plugs and wires (Bosch Premium).

Now before going any further let me tell of my credentials so I can't be blamed for putting something back together wrong. Was a service manager for 15 years so I know my way around a car, have a well stocked tool chest and know how to use them all and as a hobby I restore old motorcycles, so I am very knowledgeable and mechanically inclined.

Now for the new problem, the miss is still there. Now the engine does not slow down when letting off on the gas. I have checked it out by putting it in neutral and coasting and the tach reads anywhere from 1500 to 2500 rpms and at times it will start out at 1500 and gradually increase to 2500. The rpms drop once the car reaches 3 mph but the idle is still close to 1000rpm, not the 750 like normal. We have a 1/2 long street that has 5 speed bumps.
I generally drive at 30 to 35 in 3rd gear and let off the gas as I approach a bump so the car will slow to 25 so I can go over the bump. Now the car in 2nd gear will maintain 27 mph with my foot off the gas...almost like it is in cruise.

Sounds like a vaccum leak to me but I can't hear anything with the old stethascope trick of a tube to your ear and I have sprayed everything with the motor running to see if the fluid would temporairly block the passage way.
Oh, no more P0304 codes either.

I'm about to pull my hair out

[CREWZIN]

Welcome to the forum.

I'm about an hours drive west of you in Lecanto.

I guess you have to classify me in the gearhead category. We definitely do have some guru's and maybe one will be along to help.
As far as your problem, have you tried messing around with the IAC (Idle Air Controller) that's located in back of the throttle body? It can be taken off and cleaned which has helped some owners and others have had to replace it.

[4SPEED]

NICE ENGINE BAY Crewzin!!!!

yes, had it off and looked it over real good and cleaned it as well. Incidentially, when I had the upper half of the intake off I looked in the runners on both sections and they all looked alike. Generally in a area like that you would see a difference if there had been a vaccum leak....one runner would either be cleaner or dirtier then the rest except if the leak had been right at the head.

[CREWZIN]

OK then, the last thing I can suggest is the TPS (Throttle Position Sensor) located right below the IAC.





P.S. By the way; once in awhile a few of us in the local PT clubs get together and meet at Old Town in Kissimmee on Friday night.

[bobs turbo pt]

i agree with crwzin about the thrttle body, i had an 86 duster which back tyhen had an idle sensor well that went bad and the car would idle at 3,000 i had to stand on the brake at stop lights lol

[Mean Green]

The TPS has been a problem with the wire breaking. With the engine running at the higher idle try moving the TPS wire around and if idle drops then the wire is a problem.

[4SPEED]

wouldn't the PCM throw a code if the TPS or a wire was bad?

I guess I am looking at 2 different problems. One I've had all along and the other just started after my work.

AH, such is the life of a car owner. Reminds me when I was in service and someone returns with a problem they didn't have till the shop worked on it.

[Mean Green]

Originally Posted by 4SPEED

wouldn't the PCM throw a code if the TPS or a wire was bad?
I guess I am looking at 2 different problems. One I've had all along and the other just started after my work.

AH, such is the life of a car owner. Reminds me when I was in service and someone returns with a problem they didn't have till the shop worked on it.

Not always. I've seen this problem a lot on the srt forums.