SURGING idle
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SURGING idle
Got a 1990 f150 with a fresh '94-up truck long block 5.0 in it. All vacuum lines are new, new motorcraft tps and iac. All other sensors are new but running without an o2 right now but have a new one laying around I just haven't installed yet. All smog and egr is deleted, all ignition components are new including the distributor. Basically everything is new on the engine.
When I start the truck it would surge like crazy from 500-1500 rpm stalling several times and eventually settle down to a stable idle. The surging problem occurs mainly on a cold start. Today having tried everything else I can think of I swapped out the computer for a known good 5.8 one and started it up. What do you know it idled like a dream and didn't surge one bit. Let it idle for a minute and gave it a small rev and just like that started surging again, though not near as bad as with the old computer.
I'm at a loss here, could running without an o2 sensor cause this? If not what else could cause a surging idle?
When I start the truck it would surge like crazy from 500-1500 rpm stalling several times and eventually settle down to a stable idle. The surging problem occurs mainly on a cold start. Today having tried everything else I can think of I swapped out the computer for a known good 5.8 one and started it up. What do you know it idled like a dream and didn't surge one bit. Let it idle for a minute and gave it a small rev and just like that started surging again, though not near as bad as with the old computer.
I'm at a loss here, could running without an o2 sensor cause this? If not what else could cause a surging idle?
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SURGING idle
Just went out and put on the new o2, only a very small surge of about 1-200 rpm after coming down from high idle. Although I'm not letting it get up to operating temp, the surging problem only really occurs on a cold start. Forgot to mention that now when I give it a small tap on the gas it revs up to 1500 rpm and hangs there, won't come down until I shut it down and restart it.
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Senior User
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SURGING idle
As an update to this thread I ended up putting my original computer back in and replaced the fpr and act sensor, the problem is now 100% gone. Not sure what actually ended up fixing it but I'm not complaining with a perfect cold/warm start idle
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FlyCool5.0
1987 - 1996 F150 & Larger F-Series Trucks
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Feb 21, 2015 01:46 PM
