another rough idle problem

[evillecutter]

i know there are more than one post about the rough idle and im going through the steps to see what i can do but i have a few questions i havent found answers to yet - the whole thing started when i came back home and the engine was running perfectly - i go for a short drive and notice a little flutter like its not getting enough gas at a stoplight - get it back home and shut it off and i cant start it back up - pop the hood and try to start it again and it revs to 2k then back to 1k but still really rough idle - cleaned the pcv valve (again) and replaced the idle control valve but no change - ordered a new fuel pressure regulator and will try that next - ive also read that it could be the intake manifold gasket or the throttle position sensor which ive never replaced either before but im ready to do both if necessary - my question is what might be the best order to replace these and where exactly is the throttle position sensor? im dreading taking off the intake minifold... side notes: no check engine light, and this has happened once before but just the low idle not the dancing around of the tach - thats whan i changed the fuel filter and put a can of seafoam in the gas tank - all good for 3 months now this - like always any help is much appreciated

[VXR]

When this happened to me it was the intake manifold gasket. It is a common problem so if you know it has never been changed I would start there.

[evillecutter]

got home today and it is running and idling fine again - i was thinking since it was intermittent it was probably not the manifold gasket but im sure its never been changed and will need it soon regardless - maybe it took some time for the computer to recognize the new intake control valve?

[Ldub]

got home today and it is running and idling fine again - i was thinking since it was intermittent it was probably not the manifold gasket but im sure its never been changed and will need it soon regardless - maybe it took some time for the computer to recognize the new intake control valve?

I'd guess that's possible, as I've never had intake gasket leaks that didn't throw a code, so...

..

[Y33TREKker]

Having only replaced the fuel pressure regulator out of the three repairs you've listed, I may be wrong about this, but I'd be of the opinion that the difficulty ratings of those three would be ranked as TPS (easiest), FPR (medium), Intake manifold gaskets (hardest).

Then again, I don't know if there's any sort of calibration needed as part of a TPS installation, so it may be FPR (easiest), TPS (medium), and Intake manifold gaskets (hardest).

Unless you already planned to do all three replacements anyway, I'm always a fan of trying easiest to hardest with the hopes that one of the easier replacements will solve the issue.

[Ala5ka]

did you actually replace or just clean your PCV? If you didn't replace it try that, 6 bucks and it just may do the trick

[evillecutter]

Having only replaced the fuel pressure regulator out of the three repairs you've listed, I may be wrong about this, but I'd be of the opinion that the difficulty ratings of those three would be ranked as TPS (easiest), FPR (medium), Intake manifold gaskets (hardest).

Then again, I don't know if there's any sort of calibration needed as part of a TPS installation, so it may be FPR (easiest), TPS (medium), and Intake manifold gaskets (hardest).

Unless you already planned to do all three replacements anyway, I'm always a fan of trying easiest to hardest with the hopes that one of the easier replacements will solve the issue.

might sound stupid but where/what is the throttle position sensor? i thought the fuel pressure regulator was pretty easy

[evillecutter]

did you actually replace or just clean your PCV? If you didn't replace it try that, 6 bucks and it just may do the trick

i only cleaned it because mine is an original and ive heard bad things about the aftermarket ones going bad often (im assuming that when you can hear the little thingy moving back and forth when you shake it its still good?) - i did notice that the factory hose clamp coming off the pcv was very laxed so i put a new one on - probably didnt do any good but it made me feel better

[Y33TREKker]

might sound stupid but where/what is the throttle position sensor? i thought the fuel pressure regulator was pretty easy

It's on the side of the throttle body, and only held on by two bolts. I took a quick look and it seems the only adjustment that even might need to be made during installation would be to the accelerator cable, so I'll rank it back at easiest of the three replacements (if only in effort and not necessarily impact on the wallet anyway)

"Throttle Position" (TP) sensor - Chapter 6 in the downloadable VX repair manual.

[evillecutter]

well its back after driving about 20 miles - the idle isn't dancing around just very low again - i guess try to change the throttle position sensor it is....

[99_VX]

Since I was having a similar issue; if your fuel filter was pretty dirty maybe you have a dirty/clogged injector on cylinder 3...

[evillecutter]

left the negative battery cable off for a night and ever since its running and idling great - been about 3 days - i wasn't aware of how sensitive vehicles with an ecu are to the calibration of the fuel system since ive never had a problem like this on any of my vehicles before (youtube will tell you its common on MANY makes/models/engines) - so hopefully this is my success story but i will post again if problem comes back

[evillecutter]

update: 3 weeks later and it started again this morning - only idling low this time so far - and i noticed that when i come from a dead stop when the engine is bouncing around on low revs the tod kicks in full gear when i take off instead of its usual 15% - then it goes back to normal - going to pick up a fuel pressure regulator after work and see if that does it - i prob should have just put that on when i did the idle control valve anyways

[jasonm621]

I have recently had the EXACT same issues... Here is the solution that i have found. First of all I replaced the intake gasket which was a pig of a job!!! I had a crack on the inside of the manifold just behind the throttle body, which make it difficult to diagnose since it was near impossible to spray carb cleaner in that area... after the replacement, idle went down to an unconsistant 900-1200rpm, much better that the 2000+rpm! after throwing a slew of parts to solve the rest of the problem (IACV,FPR,TPS) nothing helped... i even tried unplugging the power steering pressure sensor with no help... and i was getting very frustrated!
Here is what i did to get it idling at the perfect 750rpm... while the engine is idling (assuming it is hopping up and down) unplug the throttle position sensor, your idle should immediately drop to a consistent 700-800 rpm. Your check engine should be on & TOD Check light should be flashing. While your engine is still idling plug your throttle position sensor back in, then shut off the engine. Walla! smooth idle after that! Your Check engine light should stay on for 5-10 key starts then the check engine light should go out on its own. There will be a stored code after that (P0122) even though your CEL is off. i havent bothered to erase it since my idle has been perfect for over a month now and i dont want to mess with it if it is idling fine! Try that solution, it much cheaper than replacing the TPS, FPR (fuel pressure reg), IACV (idle air control valve) and the intake gasket or spending an hour of your life unplugging a PSP (power steering pressure) sensor. If you do replace the intake gasket which i would recommend if you suspect any crack, torque the bolts to 13ft/lbs NOT the recommended 18ft/lbs. Unless you really want to replace the gasket in a few years, I wish that task on no one! I had to end up taking a hack saw to the EGR tube and welding it back. there was no way i could get a wrench to turn on the seized collet nut that connects to the EGR Valve on the manifold. GOOD LUCK HOPE THIS HELPS to all who read!!!

[evillecutter]

thanks jason i'll give it a try - i still have never got a check engine light and my idle since i replaced the idle control valve has been right about 600 with no fluctuation until today (about a month later) however when i run the a/c the rpms go up about another 100 - but i fugured since it was running smoothly and not bouncing around anymore i would leave it be - gonna try your method first and then the fuel pressure regulator if that doesnt work - intake manifold is my last resort and since its intermittent im almost positive its a sensor/regulator/computer issue and not mechanical one -one stupid question: where is the throttle position sensor? anyone have a picture i cant find it in the manual