Tech Area

V6 High Idle

Question: OK, here is a new one. I drive to and from work every day 25 miles round trip. Since I replaced the timing chain and harmonic damper it has run beautifully. This week end my daughter and I went shopping stopping at various malls and stores so it was drive a little and park, drive a little more and park etc. Apparently it didn't like this regimen. After the 3rd stop the idle started to stay up around 2000 and would only start to drop after a long while. It tripped the Check Engine Light and set a code 35 or IAC problem. Once I got past 40 mph the light went out until I had to stop for a light and let her idle when the sequence started all over again with an idle at about 2,000 and the Check Engine Light tripped again until I got back to 40 mph.

With the weekend I didn't have a chance to work on her so I've been driving to work all week and there has been no problem nor have I tripped the Check Engine Light again even though I've been caught in traffic and sat at idle 15 to 20 minutes at a time. Oh yes and the idle has been at 850 in neutral every time I come to a stop. What gives? I've looked in the manual and there doesn't seem to be anything to cover this sort of situation

Answer: A 2000 rpm idle is almost always a cracked EGR pipe. Which can somewhat close up when hot. The code is set because the ECM cannot control the idle with the IAC, though it is trying.

The IAC is out of the "loop" when rpm reaches 1500. That will NOT be the problem. Don't waste any $$ on a new one.

The EGR valve tube runs between the EGR valve (on the exhaust crossover pipe) and the underside of the upper pleneum neck (red top of engine). Sorta goes around the distributor.

You want to loosen the 2 bolts that hold the flange to the pleneum just enough to slide a small piece of soda/beer can between the flange and pleneum to block any air from getting in behind the throttle plate (which causes the high "idle").

The distributor cap will need to be out of the way for access. Easiest way is to remove the 3 trunk side wires from the cap and "lay" the cap on top of the pleneum. It's simpler to reattach the 3 that are easily seen then to remove them all.

CAUTION: those 2 bolts are VERY short and if backed out too quickly/far, will fall and disappear forever!!!!

The block off plate can be left in place until another EGR pipe can be found. It normally takes several years before any engine damage may occur.

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