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1992 5.0 high idle when iac plugged in. (new iac and tps, no vacume leaks)
Hey guys. Been trying to get this s*** figured out for a while now. My truck (1992 F-150 XLT 5.0 4x4) idles high (2000-2500) when the IAC is plugged in. When in plugged, the truck idles down to 400 or so but keeps running. I've checked for vacuum leaks, the IAC and TPS are both new as I thought one of them could be the culprit but with no luck. Does anyone have any ideas? Thanks.
she ain't pretty, but she's mine.
That's not much description of the truck - the more we know about its build, condition, history, & modifications, the more-likely we can help. Click this, read the caption, & edit your signature:
When did this symptom appear (time, miles, event)? Did it appear suddenly, or progressively? Don't blindly replace parts, run the engine while sensors or actuators are unplugged, or rely on luck to fix it. Put the original parts back on, and follow the procedures in Haynes or the captions of these pics to diagnose it:
Only replace a part if it's due on the maintenance schedule, or it fails a published test. Make sure a replacement for failure passes the same test the original part failed.
Ok. So 1992 F-150 XLT, 5.0, 4x4, 5speed Mazda trans, 194k miles. I bought the truck for $1500 six months ago with current issue, no idea of prior history as my wife surprised me with it. Better? So once the truck warms up a little the idle tends to settle, but then sometimes is erratic when the clutch is pushed in and/or the truck is in neutral. Parts were included with the truck so I figured no money spent, may as well try it. Oh and no modifications, aside from cosmetic and LED lights on the brush guard.
Last edited by TCReynolds; 01-04-2019 at 05:34 PM.
Reason: Additional information
battery putting out a solid 12.8 volts, I have seen weak batteries cause this..
That's a good point. The PCM has a set of conditions it monitors and will raise idle speed accordingly. 2500 is pretty high though. But the fact that the IAC is opening means that the PCM is sending power and the IAC works.
The PCM has a set of conditions it monitors and will raise idle speed accordingly.
Battery charge level is just one condition.
Figure out what makes the IAC valve open and close and you'll be miles ahead. Pretty sure it's described in the various service manuals. Maybe even on the internet. Good luck.
01-04-2019, 06:44 AM
1992 5.0 high idle when iac plugged in. (new iac and tps, no vacume leaks)
