My moms f150 (95) efi 302 has an extremely low idle when cold. It will stall when warming up just sitting there. When it warms up the idle gets better but still a little low. Its had a recent tune up...new plugs....wires...maf cleaned etc. I bought a tps sensor for it but wanted to see what you guys thought. Haven't put on the tps yet Thanks
The IAC may be dirty/sticking not allowing the PCM to increase the idle... They have some small rubber seals in them that may be damaged if a harsh cleaner is used, be sure whatever you spray in it is throttle body safe... From experience cleaning is approx 50% effective, about as often as not they'll need to be replaced... I have loaded them up with WD40 two or three times, let soak and shook them out, that seems as good as anything.. Just wipe off and reinstall, the WD40 won't harm it... Sometimes the PCM info gets corrupted, removing a battery cable for 10-15 minutes will reset the PCM and may fix it... Generally the TPS will set a code if it's defective, of course there are always exceptions... My '96 5.0 F150 is the opposite, runs at probably 2K RPM for two or three minutes before it starts to idle down... Been that way for the over two years I've owned it...
I will pull and see how good or bad the IAC is....sticking etc.....I replaced the battery recently so the pcm should be reset. Runs great other than the low idle. Hopefully the IAC is the culprit. Thanks
I would think Comet's onto something there and would be standard troubleshooting procedure anyways. Have you ever replaced or adjusted any ECM related electronics on this engine? Also keep in mind that a TPS replacement does require a slight "clocking" of the unit so that it doesn't have a small "dead spot" or lag until voltage changes. This causes the PCM to delay what should normally occur(timing/fueling) immediately during micrometer levels of throttle movement. Use a 12 volt tester to dial it in for immediate response.
One thing I didn't mention is checking base idle, should be slightly less than the stated warm idle(probably around 550)... If you're not familiar with base idle it's checked without the IAC connected, warm engine, adj just like a carb... Note kinda sounds like yours is operating on only the base idle... There really should not be a lag in TPS voltage but doesn't mean it doesn't happen... It is checked after setting base idle to be sure it's in the .6 to .9v range, then check for a linear increase without dips to WOT which should be around 4.2-4.5v... There are Stang sites that will say it should be set to .99 but it really doesn't make a difference, the ECM will learn what voltage to use as idle.. There are probably 100s of videos on the net about setting/testing the TPS... Here's one of the first I found but fordfuelinjection is also good... http://easyautodiagnostics.com/ford/4.9L-5.0L-5.8L/throttle-position-sensor-tests-1 BTW last TPS failure I had was on my '93 Lightning, had about as much power as a 6cyl with a couple bad plug wires...
