Two day's ago my 86 F150 (302 EFI) started idling high. I don't have a tach, but I'm guessing 1400-1800 rpms. Figured it was a vaccume leak and didn't worry about it till yesterday.

Yesterday, no vaccume leak found, and the truck was fine driving for about an hour, then started randomly idling high. If you hit the gas it would stay high for 20 - 30 seconds then return to normal. Sometimes it would be idling normal, then stumble, then shoot up for 20-30 seconds.

All sensors are less then 12k miles old except egr, iac and knock.

I figured it was the iac, but I replaced that but it's still doing it. I won't have time to scan the truck till tomorrow, maybe later tonight, so I don't know if there are any codes.

Other info that may be usefull. 060 over shortblock that's got about 50k on it, heads have 10k on them, AOD trans, fuel system is new (tank pump, HP pump, both filters and FPR). When I did the heads I changed Engine coolant temp sensor (the one for the computer), Air intake temp sensor, MAP sensor, O2 sensor, cleaned all the ports in the intake. Blocked EGR, No Smog pump.

Truck was running fine before this. Also truck has 200k miles on it.

I'm disconecting the battery to see if that clears up the problem. (I know it will clear codes, but if the problem comes back so will the codes. My cousin has a scanner, so it's no big deal to scan it, I just have to have the time to go to his shop.)

Just looking for ideas. I'm thinking maybe the computer is going, but I'm not ruling out something like a bad ECT sensor even though it's new...

Thanks,
David

 

Hey 100beater,
Jion the club!
MY '86 5.0 EFI has been doing that for 4 years now. Changed everything under the hood, and it still does it. 2 dealerships later, and no luck.
I'm with ya bud. I'm looking at a '86 rust bucket that "runs good" I'll buy it to compare what's going on.
Reamer

 

My 85 302 efi would surge too, but it would idle down too far every once and a while and die. I turned up the base idle screw (under the black plastic cap) It smoothed out. I also looked at the throttle body to see if any corrosion had formed. I'd run the scanner on it. My first guess would have been the IAC, too. One last thing, How's your air pump working? Maybe the short hose on it has a tear?

 

Air pump isn't working. In fact it's not even there... Ports have been plugged.

Truck has always randomly stalled when started warm, but this is a first for high idle.

I've "rebooted" the computer and so far it's not idling high. It did stall on me a few times, but that seems normal to me when you reset the computer on these cars. I guess that I'm too used to my plug-and-play computer now that the technology pretty much works... Forgot that it's a good idea to clear the computer when changing parts.

I will keep you updated. I will be puting about 70 miles on the truck on thursday (70% highway, rest stop and go) and I'll be waiting to see if my high idle deamon returns.

I have to say that I've grown quite attached to the truck over the last three years that I've owned it. It has that "Patina" that they talk about in the magazines, that rough around the edges charactor that evokes respect from other drivers. They don't drive crazy around me because they're not sure that I would bother to avoid them. The truck just screams "go ahead.... make my day..." It's very peaceful to drive.

I've put a little over 30k miles on it and I hope to put alot more on it. I just hope it doesn't start doing dumb and highly annoying things.

Cheers,
David

 

At least yours can run without overheating bubbling out of the overfill and not stuck driving a 1980 Mercury Colony Park damn boat

 

New radiator, WP, T-Stat and fan clutch = Doesn't over heat. Even when it was 102 here a week or so ago, didn't overheat.

The truck is black and doesn't have air... So me overheating was another issue...

So far so good on the idle. I'm making my weekly trek north today so we'll see how it goes.

David