Idle time

My first post, so here goes....
My 1990 F150 5.0L has a history of erratic idle problems. Especially when load is introduced. (i.e. A/C)

Last remedy included a newly remanufactured and programmed ECM and a new throttle position sensor TPS. Picked up from shop and was working pretty well while engine is hot, but found the next day after truck sat for a day in the driveway, and started cold. While engine was still warming up, I applied normal A/C and when compressor cycled on, idle dropped and recaptured. When compressor cycled off, idle increased, then settled back to normal. Repeated until fourth cycle and then engine failed to capture rpm and died. Took it to technician, he said computer needed to "re-learn", drive it and after a couple of days it should be okay! I drove it that same day and it seem to operate okay! I must assume it is still learning?

EGR, (4) ECM's, (2) TPS, NAPA Ignition module, cap, rotor, plugs & wired have been changed. MAP sensor has been ruled out at two different garages.

Any thoughts? Ideas!?

And thank you all for your help! I look forward to helping others with their questions should I see a problem that I have been through successfully!

qdeezie

Hey, I'm a new member here as well and I have a 1990 F150 with the 5.0L engine and dealt with idle quality issues. First, try pulling your IAC Valve off and cleaning it out with carb cleaner and see how your truck responds. If it responds positively to that, you might want to consider getting a new IAC Valve depending on what you feel comfortable with doing at this point. 2nd, I found that my truck was severely lacking in the electrical department as far as how well it was grounded and how well the alternator charged. I did some research and ended up performing a 3G alternator upgrade (did some research and bought just about everything at a pull a parts salvage yard) and it responded VERY well to that. Honestly, it ran like an entirely different truck. Seriously. I didn't have the slow/sluggish startup issues anymore and I didn't have the increasing/decreasing idle problem anymore and didn't cut off when run at low speeds or under a load anymore. So, you might want to check your alternator to see what kind of juice it's throwing out. The factory 2G alternators will make you go absolutely nuts with their notoriously insufficient output. The insufficient output leads to so many other problems. Regarding the ground, this was another big overall performance improver too. I removed the short skimpy wire that runs from the ground post to the frame in front of the battery and upgraded it to a 4 gauge wire. Next, I took another 4 gauge wire and ran it from the battery to one of the bolts on the throttle body. It also made a world of difference in idle quality and the odd thing about upgrading the ground to these 2 points was that my transmission shifted way smoother. In addition to the idle quality, I had a problem with the signal light indicator on the inside not coming on and the upgraded ground solved that too. These improvements alone make me so glad I bought hydraulic wire crimpers. Another upgrade I went on and done since I saw how well the truck responded to this was to upgrade the hot post on the battery from 6 gauge to 4 gauge and yet again, it responded positively to this upgrade.....I don't know if any of this will be helpful to you, but since I own a 1990 F150, I thought I'd share my experiences with this truck thus far with you. I've done other things to the truck in search of a better idle, such as a Jegs peformance ignition coil, Accel Distributor Cap/Rotor, Autolite Professional Wires, Bosch Platinum Plus plugs, but the thing that cured my idle problem was the alternator upgrade and the ground wire upgrade.

qdeezie

Other items to check would be your fuel pressure regulator and fuel filter. I forgot to mention those.

jun_ior50

I agree with qdeezie. Check for carbon and a stuck valve in your IAC. Normally some brake clean will clear it out. Not too sure if this could be the issue, but I would also check your coolant temp sensor. If the sensor isn't reading right it'll cause the the ECM to run rich. I've had a sensor go in some of my 5.0's and they ran like crap (rough idle) until it warmed up.
The sensor is just a shot in the dark, hope it helps though.

qdeezie

That's good to know about the sensor. It's a cheap part to replace as well.

sanctified

I have been having the same issues on my 90 5.0 auto 4x4. I thought it was the IAC but when I pulled it off the truck immediately died so I ruled that out. I don't know what I'm doing but read somewhere that it might help to clean out the throttle body so I took off and found that it was filthy. I polished that and as much of the intake manifold I could reach with my sausage fingers and replaced the TPS and it has run really smooth since. I did that on this past Monday and have driven it about a hundred miles so far. I runs as smooth as my wifes camry.

my .02.

Idle time

Thank you all for your replies! To address the posts I have received to date. I will look into the altenator upgrade as I have removed and replaced (R/R) the ALT with a NAPA brand RAY 213-3061K 80 Amp Remanufactured. Don't know if that is 3G or 2G? Looked it up at NAPA online store and description says nothing about 3G or 2G. I will look at my grounds and consider implementing the 4 gauge ground replacement and addition of run to throttle body.

I have cleaned the Air Bypass Control Valve. Have had it R/R in the troubleshooting phase at the mechanic. No change.

The throttle body has been cleaned (wasn't even dirty) and the TPS has now been changed twice. Evidently failed about two years apart.

The new ECM seems to be working out at present. I find that the idle is beginning to run more consistently now that I have driven it for a few miles for a couple of days. I will keep you all posted on whether or not this ECM (combined with the TPS) is the fix!?

Again, many thanks for those of you that have replied! Please, if anyone else has or has had a similar problem, feel free to comment. Especially on th ECM having to "learn" my vehicle driving habits since replacement or after having disconnecting the battery power for a time...

Idle time

Forgot.... I will look into coolant sensor R/R, should I continue to have issues with erratic idle. Thanks for your post as well!

qdeezie

Glad to see it's starting to run better for you. The 80 amp alternator is a 2G alternator. Since you have a reman alternator, you may be ok. The 3G alternator is 130 amps and did not come from the factory on the 1990 F150. It's an upgrade with parts from ford cars made in the mid to late 90s. Shoot me a note if you would like more info on it in the future. The ground wire upgrade is an extremely cheap upgrade with tons of benefits in my opinion.

Keep us posted on how your idling issues!

techrep

iTrader: (1)

There are 2 sensors on your throttle body... Throttle pisitioning sensor and a Idle control sensor..both are around $50.00 at auto zone. Had the same problem and tried cleaning to no avail...changed both sensors and cleaned the throttle body and problem solved...although you may have something else going on. Good luck and let us know.