'95' 5.0 won't idle
 

Was looking to see if anyone had any ideas on a '95' 5.0 with 5-speed that won't idle. When at an idle, the idle varies from 800 down to 300-400 rpm and enventually it will die. Car also use an incredible amount of gas, like almost half a tank driving about 70-75 miles.
Car has 82k on it, drives fine and engine runs smooth and has plenty of power above an idle. Replaced air cleaner, plug wires, plugs, idle compensator, O2 sensor and cleaned mass air. There is an exhaust leak before the O2 sensor. Could that be the problem? No one seems to want to tackle welding it since it is in a difficult place to get to on top of the pipe. I was thinking about putting a muffler wrap on it to stop the leak just long enough to see if that's what's causing all the problems. Any help would be appreciated.

Check your TPS voltage at idle, it should be around .9 to .95.

Have you changed your MAF? My MAF went bad and I had idle problems.

TPS voltage should be set to .995, but it does not really matter in this case.

A bad exhaust leak will cause bad gas milage so get the header flange tightened up as soon as you can. However an exhaust leak will not cause a roaming idle. Have you checked the EEC for codes? Are you sure you are getting proper EGR function?

Does the idle search and eventually die when the engine is cold, luke warm, hot, or always?

I think this may be the first time I've ever disagreed with you, Scott, but I beg to differ on your TPS recommendation. While it is acceptable for a SD 5.0 Mustang to adjust the TPS that high, it is not advisable for a MAF 5.0 Mustang to exceed .95vdc. The MAF TPS has a narrower range, and the ECM is programmed to respond sooner than with the SD TPS. .995vdc will work, but is much too close to the 1vdc point for my tastes.

Anyway, I would suspect an EGR problem or a vacuum leak. They both will cause a rough, stalling idle, but have little or no effect on above idle drivability. The IAB valve should be inspected as well, especially if these symptoms go away after the engine warms up.

Take care,
-Chris

I see in your sig you have a 75mm MAF. If its a Pro-M and you've got a calibrator, check your voltage. Your idle will will bounce if you get much above .9 VDC (higher is richer). That would also help explain poor mileage.

opps scratch that. That was 95mustanggt's sig.

REPLY......
 

9 mustangGT: I will check TPS voltage to see what it is
(I seem to have lost my five key on my notebook)

Rebel79 & Pkrwud: I was trying to stay away from replaceing the MAF only as a last resort, due to cost.
Idle is bad always, hot or cold.

Vacuum is OK, But will check EGR valve when I get back.

Unfortunately I got called out unexpectantly and am on the road in Phoenix.

I appreciate all your responses, Thanks.

Hmm...

I know this is not the place to debate it, but I have gotten rid of idle surges resetting the TPS from .95 to .98 or .990. And I noticed more throttle responce. Maybe its just the couple of cars I have worked on.... who knows.