I have a high idle between 1500-2500 rpm with the engine warmed up. Afyer a 10 mile drive, I got a brief check engine light, and it set a code 35, which is IAC according to Haynes manual.
Since I recently wrestled the wire bundle between the valve cover and the intermediate intake manifold during my valve lash adjustment, and I cleaned the throttle body while it was off for the cylinder head work, I'm not real surprised. Is there any way to test the IAC valve before I fork the cash for a new one? I doubt it will be cheap, and I'd hate it to be a cut wire instead after replacing the IAC valve. Any tips for replacing one? This is a first for me.
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10:21 PM
PFF
System Bot
mrfiero Member
Posts: 9017 From: Colorful Colorado Registered: Mar 99
I doubt that your IAC valve is bad.....it's possible, but doubtful.
A code 35 is almost always a vacuum leak of some sort. The most typical being the EGR tube, but a cracked plastic vacuum line will also set the code.
Since you say your idle is 1500-2000 RPM, I would take a good look at the EGR tube and those huge tubes that connect to the throttle body.....since you say you removed the TB, it's possible that one of them isn't seated properly.
Disconnect the battery to clear the codes and drive it around some more before spending any time looking for a problem....sometimes a code 35 will just go away.
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10:43 PM
2birds Member
Posts: 1685 From: Ottumwa, Iowa USA Registered: Nov 1999
It warmed up and idled fine while I was setting the timing. It didn't start idling fast until I'd driven about 5 miles or so, at 70+ mph, then it did it for the next 15 miles or so, until I got it home and checked for codes. It had no codes set yesterday, so I know this isn't a past stored one.
I will double check for vacuum leaks, though. I double checked the hoses at the TB when I reassembled a couple days ago, and I don't think they can be swapped, due to different sizes. The rat's nest of tubing is a real PITA. When my EGR tube cracked 11 years ago, it idled at 3500 rpm.
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10:53 PM
Joe Torma Member
Posts: 3485 From: Hillsborough, NJ USA Registered: Jul 2001
The reason you don't see a code 35 until you've driven several miles is that the ECM will only set a code 35 when it is in closed loop mode.
All a code 35 means is that the idle has been more than ~100RPM over standard for about 30 seconds continuously. The check engine light should go out within a couple of seconds after you start moving again.
Like Mike said, you need to check your EGR and vacuum lines very carefully, it doesn't take much of a leak at all to cause the problem. When this happened on my 2M4 I found a 1/4" tear in one of the vacuum lines, it was enough to cause an idle of around 1400RPM and the code 35's. Do NOT try to work around the problem by tweaking the idle screws.
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10:16 AM
2birds Member
Posts: 1685 From: Ottumwa, Iowa USA Registered: Nov 1999
I priced IAC's this morning. TOMCO at Discount Auto is $35, GP Sorensen at Advance Auto is $29. Advance can get the AC Delco IAC for $35 next day delivery, so that's definitely the route I'll take if I need to replace it. Haven't had a chance to check for leaks yet.
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11:05 AM
2birds Member
Posts: 1685 From: Ottumwa, Iowa USA Registered: Nov 1999
I did wire checks from the computer through the IAC coils; got about 55 ohms through each one. All vacuum lines pass a drop test (good ol' MityVac!). Started it and let it idle with the intake hose removed, and put my finger over the IAC bypass hole, and idle instantly dropped to 1200 rpm. Pulled the IAC out and it was covered in black crap. Cleaned it and the housing out with brake cleaner, and it was no longer sucking tons of air through the bypass hole. I thought, great, problem solved, but once it got to normal temp and went closed loop, it set the check engine light again and the idle went back to 15-2500 rpm again. Got the handy length of hose for a stethoscope, and I can definitely hear a large amount of air being sucked around the EGR pipe insulation, at the EGR valve end.
Put that in your cracked (EGR) pipe and smoke it... The nuts and studs for the pipe and the EGR valve itself are all nice and rusty (all 4 of them).
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06:25 PM
2birds Member
Posts: 1685 From: Ottumwa, Iowa USA Registered: Nov 1999
Believe it or not, the EGR pipe came off without any more broken bolts. First non-metric fasteners I've found yet on this thing (3/8"). And, it has a nice crack about 3/8" long inside the corrugation near the lower flange. Are these things still available? Do they require your firstborn as a down payment?
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11:15 PM
mrfiero Member
Posts: 9017 From: Colorful Colorado Registered: Mar 99
I just had a very nice used one up for sale, but it's already sold. Try GM.....I believe they are around $75 or so. If you have a part# you can try http://www.gmpartsdirect.com They sell at cost, but the shipping is steep (that's where their profit is).
Don't forget to replace the little gaskets if they are thin or damaged.
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11:28 PM
2birds Member
Posts: 1685 From: Ottumwa, Iowa USA Registered: Nov 1999
EGR Gaskets were definitely toast. The tube was last replaced under warranty in 1990.
Thanks to all who steered me away from running out and buying a new IAC to throw at it. It needed cleaning, but hopefully the EGR tube will finally end this game.
The nuts and studs for the pipe and the EGR valve itself are all nice and rusty (all 4 of them).
