2000 rpm at startup

[20GMC00]

I have a 1999 Ford Explorer Sport 4X4 Sport 4.0 OHC that idles at 2000 rpm or sometimes a little higher every time I start it. It doesnt matter if the engine is warm or cold. It idles that high for about 4 or 5 seconds and I really dont think it is good on things to start at that speed. Any ideas? Thanks.

[danielsatur]

It's probably time to clean the MAF, IAT, IAC, and throttle body.

[20GMC00]

I have done all of the above and it did not help. But when I unplug the IAC, it starts and runs like new. What does that mean? Thanks

[shorod]

That probably suggests you have a vacuum leak or a bad MAF. If the MAF is bad, I'd expect you to have a diagnostic code for that. If you have a vacuum gauge see what you have for vacuum after the idle slows down. If you have a scan tool with datastream mode, see what the short and long term fuel trim numbers are showing.

-Rod

[20GMC00]

I do not have a vacuum gauge. I will have to get one. It has a pending code, P1506 that I did not notice earlier. This is what everything was at most of the time at idle. They were jumping around alot. Thanks.

ST FTRM1 -3.1
LT FTRM1 8.5
ST FTRM2 -3.9
LT FTRM2 0.7
RPM at idle 1350
MAF .980
TPS 20.3

[shorod]

The fuel trim numbers are not out of spec, but the LTFT for bank 1 would suggest that bank is running a bit lean. You may want to check for vacuum leaks that would effect that bank, maybe around the intake manifold.

You mention you did everything suggested in post #2. Did that include the throttle body cleaning? If so, where the datastream numbers listed before or after that cleaning? Assuming your TPS value listed is in percent, 20.3% seems pretty high for idle. You might have something preventing the throttle plate from closing completely (I'd expect something below 10%), or the TPS sensor may be out of tolerance.

Factory spec at idle suggests the hot idle speed should be 750-830 rpms, MAF should be 0.6-0.9 V, and throttle position should be 0.57-1.27 V. The manual does not specify the TP in %, but if we assume the TP will go from 0-5V, 20.3% would be 1.015V which would suggest you're within spec there, even for hot idle. I'd still be checking to make sure the throttle plate is closing almost completely and checking the linearity of the TPS sensor, then I'd check for vacuum leaks.

-Rod

Originally Posted by 20GMC00

I do not have a vacuum gauge. I will have to get one. It has a pending code, P1506 that I did not notice earlier. This is what everything was at most of the time at idle. They were jumping around alot. Thanks.

ST FTRM1 -3.1
LT FTRM1 8.5
ST FTRM2 -3.9
LT FTRM2 0.7
RPM at idle 1350
MAF .980
TPS 20.3

[20GMC00]

The intake is spotless and the sensors are new. I replaced them when I replaced the engine.
Will it hurt anything to leave the iac unplugged till I have time to figure it out?

Originally Posted by shorod

The fuel trim numbers are not out of spec, but the LTFT for bank 1 would suggest that bank is running a bit lean. You may want to check for vacuum leaks that would effect that bank, maybe around the intake manifold.

You mention you did everything suggested in post #2. Did that include the throttle body cleaning? If so, where the datastream numbers listed before or after that cleaning? Assuming your TPS value listed is in percent, 20.3% seems pretty high for idle. You might have something preventing the throttle plate from closing completely (I'd expect something below 10%), or the TPS sensor may be out of tolerance.

Factory spec at idle suggests the hot idle speed should be 750-830 rpms, MAF should be 0.6-0.9 V, and throttle position should be 0.57-1.27 V. The manual does not specify the TP in %, but if we assume the TP will go from 0-5V, 20.3% would be 1.015V which would suggest you're within spec there, even for hot idle. I'd still be checking to make sure the throttle plate is closing almost completely and checking the linearity of the TPS sensor, then I'd check for vacuum leaks.

-Rod

[20GMC00]

And yes, the throttle plate is closing.

[shorod]

In your first post you mention it idles high, hot or cold, for 4 to 5 seconds. What does the idle speed drop to after 5 seconds?

I shouldn't hurt anything to leave the IAC disconnected, but you may find it difficult to get the truck started, or keep it running, when the engine is cold with the IAC disconnected. Also, if you are using the air conditioning, the engine may stall at idle if the A/C compressor engages. Additionally, if you turn the steering to lock, such as when turning in to a parking spot, the engine may stall with the IAC disconnected. When that happens, your power assist for the steering and brakes will go away. When parking, that's a bad time to loose power assist.

Since disconnecting the IAC causes the idle to drop, that suggests that the IAC is still functioning. If the idle speed drops to 800 rpm or less after 5 seconds have elapsed from the time you started the engine, I would not suggest disconnecting the IAC. I'm also not terribly sure that there really is a problem. Next time I start my Aviator I'll have to pay attention to see how it reacts.

-Rod

[20GMC00]

After the 5 or so seconds it goes down to 1200 then about 900 in gear


[/b]

Originally Posted by shorod

In your first post you mention it idles high, hot or cold, for 4 to 5 seconds. What does the idle speed drop to after 5 seconds?

I shouldn't hurt anything to leave the IAC disconnected, but you may find it difficult to get the truck started, or keep it running, when the engine is cold with the IAC disconnected. Also, if you are using the air conditioning, the engine may stall at idle if the A/C compressor engages. Additionally, if you turn the steering to lock, such as when turning in to a parking spot, the engine may stall with the IAC disconnected. When that happens, your power assist for the steering and brakes will go away. When parking, that's a bad time to loose power assist.

Since disconnecting the IAC causes the idle to drop, that suggests that the IAC is still functioning. If the idle speed drops to 800 rpm or less after 5 seconds have elapsed from the time you started the engine, I would not suggest disconnecting the IAC. I'm also not terribly sure that there really is a problem. Next time I start my Aviator I'll have to pay attention to see how it reacts.

-Rod

[shorod]

Okay, yeah, that does still seem a bit high. Back to checking for vacuum leaks. In gear at 900 rpms is the engine idling smoothly or is it a bit rough? From post #3 it would seem as though it idles smoothly.

-Rod

[20GMC00]

Runs great. Like new

[20GMC00]

Does the unplugged iac affect the MPG?

[shorod]

The IAC really only comes in to play at idle, so unless you spend a lot of time at idle, it should not have any impact on fuel economy when unplugged.

-Rod