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Old 02-18-2011, 05:19 PM
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High and erratic idle, this is driving me nuts!

Been having an idle of about 850-1100 for the past few weeks now. This week it finally caused a DTC - P1294 target idle not reached. I've cleaned the IAC and TB and it didn't seem to help. I've also sprayed all of the vacuum hoses and connections with throttle body cleaner and the idle never dropped (had my buddy in cab sitting and watching).

I also sprayed around the intake manifold where I could access it and it didn't help at all. Is there any secret to getting to underneath the intake manifold? I checked the bolts on the top of the manifold that I could visibly see, all were ok but I know there's a bunch hidden underneath.

I really feel this is my IAC. The idle seems to erratic too be a vacuum leak and the idle usually decreases once the engine gets warm. You can watch it ramp up and down on the tach. Another test was that I sprayed throttle body cleaner into the IAC air port while the engine was running. I was able to drop the idle this way but I don't think this is a valid test becuase that would stall a normally operating engine IMO.

Does anyone know how to measure the voltages off the IAC or have any other suggestions

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Old 02-18-2011, 06:44 PM   #2
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Did you clean the TB where the plunger from the IAC fits into too? I'm not sure on checking the IAC voltage but you could pull it off the TB and turn the key to the on position and see if it moves smoothly and stays put. You could also pick up a new IAC and give it a try. If you rule out the IAC it could be the TPS going bad.

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Old 02-18-2011, 06:53 PM
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Quick history, TPS went bad last summer, I went through hell changing it out with the right part (ended up using a 01 or 03 TPS or something weird...I still don't think it was the right one). I also pulled and cleaned the TB very well. Had some idling issues before winter hit, cleaned TB and IAC and all was well and reset PCM and all was well.

The TB looks fairly clean, I did pull it last week and clean it with some carb cleaner, I didn't do any scrubbing though but I did blast the crap out of the port. I also blasted the port while the engine was running.

Great idea on pulling the IAC out while the ignition is set to ON to see if it actuating, I'll try this one tomorrow. I really want to make sure it is the IAC before spending the coin on a new one. Also, from what I've been reading a bad TPS will not effect idle?

I guess it would also be worth checking the 12v and ground references to the IAC, maybe I have a dirty ground but I find it unlikely because I'm pretty anal about that thing
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