weird idle
 

Ok guys, I've just about exhausted all ideas I've had here. For the past month or so I've been fighting the crazy P0171 code. It has resulted in new, coils, plugs, wires, - cleaned the MAF sensor, checked and inspected the egr tube. Replaced the egr solenoid and valve. Replaced all vac lines and finally the fuel pressure regulator. And thank the maker, the light has been off for almost a week now. Before when it would go off it would re-appear the very next day, so after many frustrating failed attempts I'm somewhat optimistic that I've beaten the code. Oh yeah in case Bill reads this, the battery cables were inspected thoroughly. Was a small amount of corrosion on the floor board where the negative cable was grounded, but other than that the cables actually looked new (slid the rubber boot off and everything). Anyways code has been off, but throughout this entire ordeal I've been getting a weird idle. Its not consistant. Sometimes when I'm at a light the car will idle like a champ. Then other times the car will actually shake (kind of pulsate) a little at idle, like when I'm at a stop light. Thing is the RPMs never fluctuate. All the gauges read normal. In fact if it weren't for the car shakin you wouldn't know anything is wrong. This is actually getting to be more frustrating than the SES light, because with all the new parts I've been throwin at her the car runs better than it ever has. Fuel economy went from low 17's to high 19's and will break 23 on the highway. I just had the exhaust inspected today for leaks. I was told for an 11 year old car that the exhaust was holdin up pretty good and that there were no signs of leaking or cracks anywhere. So I'm curious to see what you guys think.

I'd check out your fuel filter and the injector O-rings.

Fuel filter was just changed earlier last year, you think it could have clogged or started to fail already? The O-rings also were changed earlier last year when I did my LIM gasket swap. Is there a way to test the filter? I kno u r supposed to spray carb cleaner around o-rings, but like I said the SES light went off. Guess I could change em just to be safe though.

Did you ever clean the throttle body? How about the idle air control?

Let's see cleaned the throttle body when I cleaned the MAF sensor. And if the IAC is the plug on the front of the throttle body, then yeah I cleaned that to. Didn't realize it was kinda spring loaded when I first took it off, but then I remembered a thread u commented on where you mentioned that it had to be tilted slightly clockwise or something and then lined up for reinstall.

That's the throttle position sensor your thinking off. The IAC is a plunger with a cone on the end, it open and closes like a choke. If it's dirty it will not close and you have a vacuum leak.

Ooh right right. So where is the IAC on these engines?

and what is the best way to clean the IAC, or would it be best to just get another one? only a little over 20 bucks at autozone.

The IAC is right by the TPS near the base of the throttle body. Take it out and clean the cone. Or replace, your choice. make sure the O ring is good, and the seat is also clean.

Gotcha I'll take care of that right after work. Any value in replacing the PCV valve as well?

Ok so I spoke to soon. On my way home from work my old friend "SES" showed up again. I replaced both the IAC and the PCV,(had a credit on my rewards card)and the ses light is still on and the car still shakes at idle.I'm stumped.

Still putting money on the filter. For the idle no way to check it but it's only $15 for a new filter.

If it rattles it should be good, but no harm other then the cost in replacing it.

Took the car in to get smoke tested on friday. Everything checked out. No leaks. Also had fuel pressure checked. It was at 42 psi. I was told 45-55 was normal but 42 was acceptable. Hooked car up to diagnostic machine, got no response from MAP sensor. Even unplugged it and nothin happened. I mean shouldn't the car have died? Anyways replaced the MAP and what do u kno, still runin lean still shakin at idle. Diagnostic said pcm keeps tellin engine to run lean but then it richens back up when I get on throttle. Possible bad 02. The battle continues....

Ok guys update time. Turned out my engine was not likin the 42 psi that my fuel pump was runnin. installed a new pump and fuel pressure is back well within the suggested psi. now my oh crap moment. discored a leak at the base of my supercharger. the new pump although it made the car idle a whole lot smoother didnt completely solve my p0171 issue. so i was randomly spraying carb cleaner, hit the base of the SC right inbetween 2 of the injectors and i heard the idle change. looked a little closer and the zzp gasket that was on there has a bit of overhang, it was enough to keep it sealed during the smoke test but twhen i pulled it down a little and sprayed, definite leak. so needless to say got a sc gasket change comin up here soon. HOPEFULLY this will resolve the issue. im goin on a full month here dealin with this thing. I'll post pics of the engine when im done, thing looks brand new with all the new parts she's gotten tryin to fix this thing. keep u posted.

This is why I make my own supercharger gaskets.

Oh yeah i forgot u were doin that dan. What are you using to do that?

Moved to Mechanical/Bonneville/2000-2005 for better visibilty and search engine indexing.

Ok so time for another update. So the last time, my mechanic friend had found a leak under the supercharger gasket. (Still waiting for the new gasket.) Anyways today i took the car for an alignement. Can someone please tell me why after the alignement, the engine light went off and the car now drives better than it has in months? now let me preface this by saying that every time prior to this that the engine light went off, the car would continue to run like crap(weird idle and what not) and eventually the light would return. also as it has been runnin lean my fuel economy has been through the roof. however this time, the light went off, the idle smoothed out and my fuel economy has gradually dropped back to what it was before this whole nightmare began. now im no idiot so i know the alignement didnt caue this new revelation, but you gotta admitt that the timing is pretty amazing. now i should also mention that thursday i changed the throttle position sensor. however after the install it still ran rough and the light was still on. likewise prior to the alignement the light was still on and it was still running rough. i have to say this has been the most bizzare code i've ever dealt with on any car. like i said still got a new SC gasket comin and since i've already paid for it, still plan on goin through with the gasket swap. as for right now she's running pretty good. i have no idea what to make of this. let me know what you guys think.

Hopefully this will be my final up date on this issue. Last time i was talking about doing a supercharger gasket swap. well that has finally been done. have a look at what we found.

Attachment 18186

GAsket looks pretty much shot, but thats not even the best part.

Attachment 18187

yes that is a rip in the gasket. No clue how it got there, but i do know it wasnt there when i put it in. Im thinkin when i had my accident, my car was left at a pretty steep incline(sideways) dont know if it is possible for some coolant to have overun the LIM and swamped the gasket, (only thing i can think of) and made it all soggy.

anyways the projecty was a success. No more rough idle, but more importantly no more P0171. heres a few pics of the engine bay all put back together and with new valve covers. the rear cover had been leaking for a while so i finally decided to knock it out while the engine was in pieces.

Attachment 18188

Attachment 18189

Good to hear you got it. Lets hope it stays that way.