Yet another surging Idle problem...

I used to have that problem years ago on my 87 Mustang GT, and now I got it with my 02 GT.

This time it's is a bit weird I must say. The surging happens whenever I turn the on the A/C.
At first I thought about a faulty sensor related to the A/C system but I just discovered that the problem also happens with only the blower on. (no A/C)

The surging goes from idle to 800 rpm, but its very "precise" in it surging, meaning it heads right away for 800 then back to idle and so on....

So I have 2 questions
1) Any hints on what to look for ?
2) Can we pull the codes like the old day using a test light or multimeter on these cars ?

Thanks

OK, I just cleaned the air bypass valve with carb cleaner. Still doing it.
Also after looking, the surge is from Idle to 950 rpm.

Your air bypass valve is an Idle Air Controll Motor...

Suggestions: Test the voltage going to and coming from your TPS. Someone or some book close to someone will have the relative values to look for but you need jumper wires.

Question: When it's just the blower and not the A/C are you SURE it still surges? Becaue if it's on Defrost, that will engage the A/C clutch and activate the Air Conditioning system, the heater controll switch shouldn't point to anything showing the windshield.


FE
[addsig]

Thanks Falcon, I didn't know that using the defrost would engage the A/C clutch. After testing again: Blower only, no problem. A/C or defrost it surges.

Also, the A/C is not as cold as it used to be. Even when set to "max A/C" it barely cools the car to a comfortable temperature. Maybe this has something to do with it.
I will definitely check the TPS Voltage and post back the results

Thanks

You can pull codes with a code scanner. I would buy a better one with a LCD readout. It's kinda a pain in the butt to count the beeps but not to bad. The jack for the code scanner is by your driver side strut tower.

I would look into replacing your ACT and ECT sensors.....if you havent already.
[addsig]

There are IAC restrictior plates that are said to cure this problem.
Try these sites:
http://tinyurl.com/n2avp
http://tinyurl.com/rfa8v
Try this, you can even get some fiber gasket material from AutoZone to make your own, before you spend money on the real thing. You will only be out a little time and the cost of the gasket material. If you have hole punches, that is a plus, if noy use a xacto or box cutter to cut the holes. Good luck, Chris.

It sounds like your A/C is cycling on and off. When the compressor comes on it kicks the idle up. If it is low on freon it will cycle more frequently. This would also explain not being cold enough. Turn A/C to off and ssee if it still does it. Look for vacuum leaks also.

Your IAC(idle air control valve) may still be flowing too much air when the duty cycle increases.

Has the idle ever been slow to return after you rev it?
If you have a manual trans., do the RMP's hang between shifts?

If so you may have too much air flowing through the IAC.
Try this...next time it surges, unplug the IAC and see if the RPM's drop. If they do, you may need a IAC restrictor plate to even the idle out.
Good Luck, Chris.

Thanks for all the answers.
I think that rcm600's answer make sense.
I'm going to have that A/C fixed, checked for leaks and fill the freon (or whatever the stuff they use now ! )

Then i'll try the other suggestion if that doesn't fix it.
Thanks again
Phil