High Idle - Possible bad IACV?

[HappyCarGuy]

Been chasing this issue for a while and can't seem to fix it - I'm about to throw in a VG33 and call it a day. Been on MitchellDIY, Youtube, this forum, and every other place I can think of.

'94 XE manual:

 

Initial symptoms: About 5 weeks ago, I noticed that the car would just die upon pushing in the clutch - idle surge between 500-1000, but would drive down the road just fine (until the clutch was depressed). It started as once every few days, then became more consistent to at least 5 times a trip. 

 

> IMPORTANT NOTE: replaced IACV as kind of preventative maintenance last May with Bosch 64221 IACV.

> I thought it could be the EGR solenoid (started with cheapest first), so tried just unplugging it for a bit. In doing so, of course the CEL was tripped; however, the car NEVER died in CEL-on mode. (CEL was EGR error and knock sensor - nothing else)

> Plugged EGR solenoid back in, CEL went away, but car occasionally would still die, just like before. 

> Checked/swapped MAF with one that I know to be good - did not make a difference. 

> Replaced those smaller intake tubes going to EGR solenoid and other locations in case of vacuum leak - made no difference

> Replaced intake tube between TB and MAF - made no difference

> STARTED GETTING DESPERATE: Replaced throttle position sensor. When I put in new one, at .40V, car idles between 1500-2000RPM. However, at around .20V, idles perfectly fine around 750RPM

> Have done MULTIPLE exterior vacuum leak tests - cannot find anything externally that impacts anything.

> I tinkered with the idle screw - turned it all the way until it bottomed out to lower RPM, and only got it down to 1300, so I just adjusted it to how it was before (I kept track of the turns knowing that this probably wasn't the issue)

> can pinch off vacuum hose going to IACV and the other little solenoid (I can't remember the name of it at the moment, but I replaced that about two years ago as well) at the little 90* elbow and car will idle about right at .40 TPS setting -- MAYBE A DUMB QUESTION, BUT IS THIS INDICATION OF BAD IACV, OR IS THIS NORMAL??? Pinching off AFTER Y-tube (to IACV and other that other solenoid) to the other solenoid makes no difference, so I know that that other solenoid is functioning/doesn't have leak or anything

 

> After replacing TPS and adjusting it to around .20-.25V, car runs perfectly fine and does not die or have idle surge. However, I know this is out of specs for that sensor. I'm kind of at my wits end - do I leave the TPS at .20-.25V and just send it (as the cool kids these day say), or should I attempt to diagnose possible IACV or other issue? Before I drop another $200 on that valve, are there any quick tests to run on it? Would IACV already be going out after just one year? No check engine light is on - all systems seem to be just fine. Would a mis-timing of the distributor (either retard or advance) cause an issue like this - maybe it got twisted or something while I was changing the TPS?

 

Any directions would be appreciated!

 

Edited May 14, 2023 by HappyCarGuy

[Frenchy]

It does sound like you have a bad Idle Air Control Valve. That said I would suggest going into the Factory Service Manual and looking at the Symptom Diagnosis charts. It will drastically help when diagnosing problems before just replacing parts.

[HappyCarGuy]

Update to this age-old post: turns out it was a malfunctioning Pulse Air Valve (goes by a couple of different names, but the part number is 22660-5210V). It was kind of a weird replacement, because it met all test procedures - just kind of stumbled upon it while running some other tests:

 

According to manuals, you are to measure the resistance of the two pins and if it is between 70-80ohms and as long as it checks out, you move on to diag'ing the harness etc. Apparently my solenoid was still functioning (I think it was around 72-73ohms) but something was causing the valve to not close as much as it should (possible worn internal spring?), thereby sucking in a bunch of unwarranted air. This was accompanied by a strange "air surging" sound coming from the intake - almost sounded like a dang vacuum at the air filter. I diag'd it by removing the two 10mm bolts and plugging both the intake plenum hole and also the valve itself. The "vacuum sucking" sound stopped at the intake and the idle mellowed out. 

 

Anyway: if anyone has this bizarre issue, and the intake sounds like a vacuum or 'surging/sucking' sound, it pays to firstly unplug your IACV (easy test - if your idle drops, you know it's okay), then check that pulse air valve/air regulator. Especially if you can find no other exterior, other vacuum leaks in any of the other hoses/tubes. 

 

hope this helps someone. 

[Frenchy]

Good to know and appreciate the update. Just looked up that particular valve and we.lile to call it the "Cold Start Valve" since it allows air in when Cold and shuts off(closes) once warmed up enough.

Edited January 26 by Frenchy

[adamzan]

Thanks for coming back... I have a weird issue on mine where it is running incredibly lean at idle unless you give it some load then it smooths out... This part "tested good" on mine as well but since it's easy to change I might just swap it out with a JY spare.