92 F150 5.0 Poor Idle

My first question would be: have you checked for fault codes and what were they? The problem you describe would suggest a vacuum leak of some sort. This may be the common leak between the upper and lower intake or a leaky EGR valve. The resistance reading you have on the EVP sensor is only useful if you have checked it throughout it's operating range. I suspect your problem could quickly be located by a knowledgeable tech using a STAR tester. Most shops can run a diagnostic scan for about $70 on SE USA. This would be less expensive than just throwing parts at it. You can check for vacuum leaks spraying carb cleaner or similar material around joints with the engine running. WD40 also works well but, leaves a bit of a mess to clean up. Watch and listen for a change in the engine as you spray. That will be a leak that needs repair. As for testing your sensors like the EVP r TPS, a rought test can be done by using an analog meter. Watch the needle very closely as you manuall move the sensor thru it's range very slowyl watching the needle for anything other than absolutely smooth progressive movement. You can remove the EVP sensor by removing the 3 screws with no harm in most cases. It is sealed with an O'ring which is reuseable in most cases.

just checked the codes by means of a jumper wire for the self test and watched the check engine light i found:

Key On Engine Off - Code 41 - my haynes manual tells my O2 sensor - lean condition

Key On Engine Running - Code 13 - Idle Air control motor - cannot control low idle check speed during self test

As I mentioned before - new IAC motor 8 months ago. I try checking for vacuum leaks. Can an O2 sensor cause idle problems such as racing at cold start? I thought they had to warm up first? What about Intake Air Temp sensor. Some articles suggest they cause idle problems. Can you just check resistance or do you need to check voltage also on IAT?

I'm sure my local Ford dealer can fix it but I want to try a few things first - even if it costs me a few bucks.

Consistent with an open EGR or vacuum leak.

Again consisten with vacuum leak or some sort

O2 sensor is not in circuit during cold start. ECm is operating engine from internal map for first 90 sec or so.

IAC has a resistance spec. Between 9-11Ohms IIRC. Even new ons can go bad

Have you ever checked and clean throttle body? TPS or ECT -

- not guage sensor - may be bad causing ECM to operate based on incorrect engine temp. You can sort of check with ohm meter. Same is true of CAT - not converter - sensor.

|just checked the codes by means of a jumper wire for the self test and |watched the check engine light |i found: | |Key On Engine Off - Code 41 - my haynes manual tells my O2 sensor - lean |condition

That's just a symptom of the vacuum leak. Be sure to check the air intake molded hoses for cracks. Minde was cracked at the throttle body, bottom side where you can't see it.

|vacuum leaks. Can an O2 sensor cause idle problems such as racing at cold |start?

O2 sensor doesn't cause anything, it's just telling you you have a vacuum leaking which is leaning out the mixture. Rex in Fort Worth

The TPS can indeed cause the symptoms you describe with no codes set. The ECM use the TPS signal to determine throttle setting. The TPS on the 5.0 is on the bottom of the throttle body. It is held in place by two screws. There are no adjustments. Watch the engagement of the little tabs. When you remove the scrtews, it should have a little tendency to rotate a little. Turn the new one the same way to install making sure the tabs are slightly rtaoted when installed.

The easiest way to get to the TPS is to remove the throttle body which is pretty straight forward. You will probably need a TB gasket as they usually crack when they are old. You can leave the coolant hose connected or drain the cooling system if you want the extra work. This is a very good time to clean the EGR & vapor ports and, the throttle body while you can easily reach them. You should reset the ECM either using a scanner or disconnecting the negative battery cable for 10 minutes or so. When you restart the engine, let it idle until warm without touching the throttle. If it is an electronic automatic, put it in each gear position for a few seconds allowing the EMC to learn the engine idle paramaters.

Hope this works. Good luck.

Danno, Get a code scanner; $30 at most parts houses. While you're there, pick up a new TPS:-)

Randy

It needs to be set. I'm not exactly sure but I was thinking it was .5 VDC @ idle. Check your book.

Randy

The TPS is not adjustable for practical purposes on this engine. The only way to adjust it is to elongate the holes in the TPS or, change the base idle opening of the throttle blades. These are not task for someone not intimately familiar with what he is trying to do and will not affect the symptoms he describes.