Intermittant High Idle (again)

[Grif]

As posted in a different thread, I have an intermittant high idle prob. Thought I had fixed it, but its back. So far I have cleaned the Mass Air Flow (MAF) sensor and yes I used sensor safe cleaner, replaced the Idle Air Control valve (IAC), and Throttle Position Sensor (TPS), cleaned the throttlebody, checked for intake manifold gasket leaks via spraying around the manifold with carb cleaner.

I cannot rule out other vacuum leaks as I dont really know where to look or a easy method of locating them, but nothing really stands out as far as cracked or missing hoses.

The PCM never throws codes, CEL light never turns on despite idle that somtimes reaches 2600RPM! Somtimes it idles ok tho, but usually around 1000-1200. PCM appears working because my OBDII reader sends live real-time data to my Droid phone just fine. (can the PCM just partially fail?)

Here is what I have left IMHO:

Some here have suggested fuel pressure regulator. I don't know how to test this. Other forums have reported possible fuel pump itself.

Some vacuum leak SOMEWHERE, again, how to test?

One forum found a fix on a 3.5L trooper in that the power steering pump pressure sensor may be failing. On that forum the diagnoses was apparently correct. Apparently the logic goes that when that sensor gives a low reading, the PCM bumps up the idle to increase pressure in the lines. I find this interesting as the last time my oil was changed, the ppl there showed me some leakage they identified as power steering fluid. It was apparently a slow leak as it never drips on the driveway, but it was leaking around or onto the "intercooler" where it enters the radiator (lower left side of the radiator as you face the front of the VX). They showed me the evidence of the leak, it was definitely red fluid. They were not concerned as the leak was apparently small.

So... any pro-tips? I really, really do not want to go to an average joe mechanic only to have him replace all the stuff I already replaced (which to me are the obvious and easy things). Only to have to have it back the next week for the same problem. At that rate this could take months and hundreds of dollars of labor costs before its fixed.

Any thoughts appreciated.

Oh and for you ppl with Scangauge or other realtime OBD interfaces, where can I find proper baseline numbers for what I *should* be reading from data such as MAF and intake pressure?

[Ldub]

FWIW, though probably not a lot of help...

The fluid leak by the "intercooler" would more likely be trans fluid, as I'm not aware of the power steering system being run through the radiator...

[Grif]

Yeah Ldub, I was curious about that too. But the fluid was dripping onto the intercooler, not from it apparently. They seemed pretty convinced it was steering fluid.

[Grif]

Ok, put it in the shop. They were unable to find any external vac leaks. They could not rule out internal vac leaks (WTF are internal vac leaks??)

The shop found the info about the power steering pressure sensor possibly causing this, so they started to check that out, but in the process found a broken wire from an oil pressure sensor (tho the invoice indicated it was an oil pressure SWITCH) and once that wire was corrected the idel went down nearly to normal.

They were as suprised as I was.

So I got the VX back from the shop, and to me the idle is still a bit high. But at least not 2000-2600 RPM.

I had never heard of this potential cause before so I post it here. I think it will take more testing before I'm convinced because the high idle condition was intermittant anyways. I post the info from the shop here simply because it was news to me.

[Grif]

No comments? No replies? Despite the fact the I've proposed a new fix for scroggy idle probs?

Despite the fact that I requested baseline OBD measurements from you scanguage owners?


My posts have been buried. I'm feeling kinda alone here.

[Heraclid]

Mine has been doing something similar, idling around 1200 rpm, shooting up to over 2000 rpm (sometimes well over) when in neutral or park. Surging while driving, seems to be mostly during deceleration coming to a light and such. Was sitting in line at a drive-thru and it was revving up pretty good and got way hot. One time it got real hot and also had really rough transmission shifts, but only once did that happen. Inspection showed some serious oil consumption and water was low.

Had erratic idle a while back but not the surging, etc. Replaced the IAC back then, problem pretty much went away until a week or so ago when all of this started occurring.

So anyway, a little over a week ago it started surging pretty bad then getting too hot. Got a CEL when it overheated, oil & water low, changed oil, added water, new air filter while I was at it. Checked PCV, sprayed IAC and throttle butterfly valve with carb cleaner. Have not done EGR though. Has not overheated or thrown another CEL since but still was surging. Problem is intermittent, may act weird right at start-up, drive great for 30 minutes of so, then start misbehaving. Some times worse, some times not at all. No apparent leaks other than a very slow power steering fluid leak I've known about for some time. Was advised to just keep an eye on it, shop was in no hurry to replace the pump and didn't seem to think it was a big deal.

VX was finally in the shop today and the code they got indicated a faulty throttle position sensor. Would be nice if that's it because it wasn't obscenely expensive ($40 part, though that is a lot for no more than it is). Since that was replaced this afternoon it is still idling a bit high, just over 1000 rpm, but if I shift it into drive while sitting still it settles to normal idle speed. Short little drives tonight yielded no surging though, will see how it goes from here.

I forgot to tell them not to use the windows, and it seems like mechanics always do. So the window glass came off the lift mechanism, dropping the glass free into the door. Since they made no attempt to make it right after doing it and I was sort of mad about that and would pretty much just rather they didn't anyway, I had to pull the door apart tonight and get it back in place. Got that down to a science now, done it plenty. It's a wonder the glass has not broken yet. The rubber in the forward channel is totally shot and needs replacement. I like using my windows and my main gripe with the VX is I've had mine since 2003 and the windows have never worked right. Really crappy design.

[ZubrAZ]

i had nissan 300zx z32 few years back. those cars are "famous" for their cheap wiring -> easily/quickly corroding, causing very rough idle/poor perfomance. since you said there is, possibly, electrical problems, I would check the wires and connections by the wre that goes to oil pressure regulator and would shaken the other ones, particuularly the wires which power the injectors

[etlsport]

i could give you some scangauge measurements from idle, but would need more specifics. do you want a cold start? or a warm start? AC on or off?

I also have aftermarket intake filter and exhaust, so that may make a difference, let me know what youre looking for and ill do what i can

[Grif]

Thx ETL,

Mostly I would be intrstted in startup, cold start, AC off idle. Cuz thats where I start my measurements. I'm looking to get ideal baseline numbers. Your intake should not matter much since if working properly, the computer should aadjust. If you can provide more numbers such as when coolant gets above 180F or so might be helpfull.

But whatever number you can give me under both cold start and warm running driving may help..

Thx bro, I trust your opinion.

[Grif]

BTW started it up today, and it would hardly run at idle. Without my foot on the pedal, it would simply die. had the shop change plugs and fuel filter when it was there. But same prob. Drove approx 10 miles, parked for about 15 mins, started it again and it went up to 1500 RPM at idle. Revved the engine to see if it would shake back down, nope. Then drove the same 10 miles back home, on the way i stopped at several lights, it was back up to 2000RPM. Five mins later I was home and idle was perfect at 700. Let it sit for an hour or so, went out and started it up to play with some audio stuff, and it wouldnt idle below 2000 again.

This is frickin nuts.

Its going back to the shop on tuesday. I have nothing left to try from the advice from folx here but demand they replace the fuel pressure regulator. Either that or check every wire from every sensor. Its still not throwing any CEL codes whatsoever.

[Grif]

So back to the shop it went, they pulled the power steering fluid sensor off, and bam, it went back down to 1000RPM cold idle. I'll drive it a few more days and see how it goes. Luckily they didnt charge me for this re-visit.

The shop owner stated that if it were him, he would just leave the sensor off unless I was planning on racing it or somthing. I dont know if thats a good idea or not as I tend to have a lead foot.

Still, its not 700-750 which I gather is ideal. What do you all think? Leave the sensor off? (i cant imagine its very expensive, and could prolly replace it myself). And should I still demand 750RPM warm idle?

[Grif]

Awesome work ETL! That at least gives my numbers some meaning and a baseline to compare with. Yes, I'm sure your intake will effect readings somewhat, but its a start. Thanks again.

Really, seriously. That was above and beyond the call of duty. It was exactly the kind of data I was looking for. I propose a thread where we can all share our data.

[VX crazy]

I am having same problem with idle, had this last year exactly and cleaned ICV and replaced FPR (Thanks Jay) and problem fixed, but its doing it again. I just replaced the ICV in the NAPA parking lot cuz I am sick of cleaning the other one but problem not fixed so I am wondering if I should try this power steering fluid sensor people speak of....and does anyone know where it is located? I am sure near the pump but a photo would make it less frustrating for me. OR should I replace the FPR again.....what are the odds that would go bad in 1 yrs time???

[Grif]

Sorry Lisa, I'm not sure where that PS sensor is. My mechanic just unhooked it and called it good.

[VX crazy]

Grif thank you for the speedy email and photo, I figured it had to be on the throttle body LOL. This morning it does run smoother than I remember it running in a long time....maybe it was the throttle position sensor or gremlins that will pop up again in a few days or months lol