misfit6794

Issue 1- So for some reason when I have the front defroster on, my idle likes to jump between 500-1000 up and down. Idle stays perfectly smooth with any other heater setting. I cleaned the iac and maf, replaced the pcv and battery, and put it new plugs. Any ideas?

Issue 2- After my car sits for hours on initial start up my oil pressure gauge will be all the way in the red on L, after a few minutes it goes up to its standard position. On a warm start up it will always go to the normal spot it stays in. Is it the switch? I read the tsb for 99-01 mustangs that describes exactly what mine is doing, any thoughts are greatly appreciated.

1999mustang2000

wierd

livefast1

1. sounds like you have a vacuum leak to your hvac system.

2. sounds like you need an oil pressure sending unit.

Obsequious1

My 03 does almost the same thing with the rpm's jumping when the AC is on. The AC compressor uses that much HP when at idle.

misfit6794

Thanks for the replies, I'm totally new to mustangs. Would anyone happen to have a link to a vacuum diagram?

I've heard the sending unit is an absolute pain to get to, I guess I'll just be putting in an aftermarker gauge.

Xemeth

Good response. Very helpful.

To the OP, livefast sounds right. I'd say vacuum leak and sending unit.

cliffyk

If the IAC is not behaving properly the idle will jump as you describe when the AC kicks in--in fact that about the only thing that would cause that behaviour.

I realise that you cleaned it, and that some have had success in doing that, however the shop manual states quite clearly: