[bjl95mustang]

In the mornings I will stop for gas about 1 mile from my house. When I’m pulling out of the lot it will stumble when I accelerate. But on the highway it’s fine.

After I have been driving for a while and she is nice and warmed up I have some issues. When I’m sitting at a light my rpm’s will drop and I can my engine stumble. It seems like it’s miss firing. But once I’m moving she is just fine.

I just did a tune-up a couple months ago. Cap, rotor, plugs, and the wires are about 2 years old.

Where should I start checking? I have not had a CEL.

[melk]

Have you cleaned the IAC? Checked out the TPS?

[cmonson]

when this starts happening, and you don't have any codes, I would start by taking your throttle body off and cleaning it so it looks like new. This could help, and the costs are free.

If that doesn't do the trick, then I would replace the IAC, then the TPS.

On a 98 (12 years old) the TB could be very carbonated and thus create problems. Clean out the small orface very well also.

[gomes512]

stumble upon acceleration usually indicates a tps that's on the way out. You can further diagnose by idling in park and very very slowly depressing the accelerator a little by little. Usually a bad tps will not notice this slow change until you've depressed the pedal a good bit. Then it will jump up to say 1K or so, so you should see a hesitation. When this jump occurs keep your foot at that position and release the pedal very slowly to the end, it will most likely cause a rough idle.

If changing the tps I would just get a new iac to go with it, two birds one stone.