Hey everyone I am new here. Recently I bought a 1990 Ford F:250 Custom with a 351w and c6 auto. It’s a good truck aside from the problem that is idle’s high a lot. When starting it in the morning the idle jumps around. It jumps to 1,000-1,200 rpm when I put it in park and when stopping for a stop sign or something remains at 1,000rpm. I have been doing some research and some say it’s the tps, or iac, or maybe even the Egr. All the Vacuum lines look new and I suspect the old owner was trying to track this issue down as well. I haven’t had the time to try to diagnose it myself so I would like to see what some of you guys can recommend. Thanks in Advance

 

Check for codes, even if light isnt on could have stored codes, most of us use this $30 OBDI code reader, takes the guess work out of counting flashes, best $30 ever spent.

 

thanks man, I will buy one and give her a scan and see what it says.

 

So a little update on what is going on. Have been waiting for my code reader all week it’s been taking forever. I’ve noticed since it has gotten cold here in KY that sometimes when I stop and then go to start moving again it wants to stall or stalls. It did it this morning and very nearly wouldn’t start until I held the throttle open and it started fine. It never did it until it got cold. One morning it started that high idle stuff and I unplugged the tps sensor and it returned to a low idle I plugged it back up it did a little jumping around and leveled out and was good for a few days and started it again last night.

 

Search on how to test the tps. You just need a volt meter. You watch it constantly increase as you open the throttle and reverse as closing. If it starts bouncing around or falls flat as you open and close it, it’s bad

 

That’s what I just did lol. Thing was reading .68 volts instead of .98-.99 that it calls for. It read right at wot but the idle and closed was reading off by quite a bit. The new one seems to have fixed it, my guess is the guy replaced it and didn’t adjust it to the correct voltage. Thanks! Still has a few weird issues but that is at least fixed.

 

So another update on the truck. The high idle seems to be fixed. Previous owner had installed a new tps but didn’t adjust it and had also damaged it. Replaced it with a new one and adjusted it solved the idle. Now a new problem has occurred that is less aggravating, when it is cold and I go to drive it, and say I stop at a stop sign it stutters or rarely stalls. Put my obd 1 reader on it and no codes have popped up. If I let it warm up to operating temp it does great and when we had little bit of warm weather it ran just fine. Any clues on this new issue?

 

There are a multitude of things that may be causing this. When was the last time it had a good tuneup and what have you done already to try and remedy the issue?

 

I am not sure when it last had a tune up I have only had it for a few weeks now and the guy didn’t mention anything about a tune up. Of course it was warm back then and it acted fine other than the high idle condition that I solved. I do know the Iac, and egr valve have been replaced as they are new and some vacuum lines as well. Haven’t really tried anything other than a scan. Thinking of getting under it when I get home from work tomorrow and checking the O2 sensors out to see if they are new. This has me kind of stumped

 

Computer doesn’t pay attention to O2 until it’s warm. Warm up enrichment is coolant temp sensor, map sensor and tps. I believe those are the only ones.

 

Also, take a look at your IAT sensor. With the cooler temperatures, the cooler air needs more fuel to maintain the proper air/fuel ratio. At idle, it may not be getting enough fuel to maintain idle.

 

I knew there was another one!

 

Just got home from work, didn’t know I had the day off for sure lol. Anyway the problem has gotten worse, it bogs down for a split second just about time I left off the throttle and get back on it now. And when I was a mile or so away from home when I let off the throttle it drops rpms by a few hundred and stays there and even felt like it was trying to throttle up again. I am going to scan for codes again and see if anything changed. Edit: Checked and still no codes

 

Have you pulled your intake air temp sensor for a look? Do that and I would pull the idle air control to clean it/inspect.

 

I’ll give that a try, thanks