Just bought a 1998 Mustang 3.8 auto. Seller told me it dies while driving.
Took it back home about 50 miles. No problem except once after about 25 minutes of 65 mph driving, I saw the tach jump from 1500 to 3000 rpm. Engine did not ref up.
When I was pulling off the interstate, the tack again went to 3000 rpm. This time the engine bogged and the yellow check engine light flashed. I slowed down and kept it going till I reached home. Any ideas where I should start.
It has 186K on miles but looks like its in pretty good shape.
Thanks!

 

Check for codes.

 

The only code that shows up is P1729 4x4 low switch error, which doesnt make sense.
Cleared the code and went on a 20minute drive with the OBD reader plugger in. Again when coming off a ramp and excellerating it liked shifted into neutral, tach went to 3000.
Then traany caught, engine bogged down and check engine lite flashed, but no codes were registered on the reader.

 

Swap out the IAC valve and the PCV valve. The IAC valve is most likely the culprit but it usually gets gunked up due to a poor performing PCV valve. Swapping out both should solve your problem.

 

Thanks Fryguy. I've ordered an IAC. Will make the change over the weekend.

 

Curious if you put in the new IAC yet?

 

Not yet, purchased one from AutoZone. hope to install this weekend.
I'll let you know if it works.
Thanks for your help.

 

Moving this tot he v6 section.

 

While doing the engine antifreeze flush(mostly rusty water), I did a compression check on the cooling system. A large leak at the intake manifold. Before I replace the IAC valve I'm going to replace gasket. Thanks.

 

Replaced both intake manifold gaskets, found back two water ports blocked with mud (radiator sealer). Replaced spark plugs and wires. Engine runs good now. Next brakes and rotors.