Replaced IAC but still stutters at idle

After replacing the IAC (major KIA dealer price ripoff), I thought things would improve - but alas, it's less severe stuttering, but still hiccups every 20+ seconds at idle. And still, after 4 months of this, no CHECK ENGINE light, so I assume no codes.

So, now what?

BTW, while I haven't really looked, can someone point out where the fuel filter is located? (1999 2.0l engine)

After replacing the IAC (major KIA dealer price ripoff), I thought things would improve - but alas, it's less severe stuttering, but still hiccups every 20+ seconds at idle. And still, after 4 months of this, no CHECK ENGINE light, so I assume no codes.

So, now what?

BTW, while I haven't really looked, can someone point out where the fuel filter is located? (1999 2.0l engine)

have you ever changed plugs? might need tune up.

the fuellter is in the ejngine bay . lean on the left fender look past the battery towards the engine block.

Yes, it had a tune up - just before this problem developed - which has always pissed me off (KIA service).

BTW, located fuel filter, will have to wait to replace when engine is cooled down, looks like tight fit.

Yes, it had a tune up - just before this problem developed - which has always pissed me off (KIA service).

BTW, located fuel filter, will have to wait to replace when engine is cooled down, looks like tight fit.

Did they replace the ALL the wires for the coils when they did the tune up? Most people miss this part. They just screw in a set of plugs. The wires (all the wires including the short jumper harness) and plugs are changed here all the time. They get hot and overtime

I'm not able to determine if the coil packs were replace - but yes, they did do new wires. Overall, I have good performance and gas mileage, so this looks to be a idle only condition. Should I pull the top off and replace the coils anyway? I removed the MAF and lightly blew air by/around it. Also cleaned MAF plug/contacts. Will replace fuel filter today. Any other thoughts?

Pull the vacuum line off the fuel psi regulator and have someone rev the engine. Its probably leaking. If it leaks fuel replace it.

If you have a misfire it is going to throw a P0300 code for the specific cylinder.

Rarely have I had a coil go bad.

The stutter has become worse, and now it stalls (nearly) on accelration from dead stop. I still believe it is electronic, as there is no problem while in PARK, only when in gear (D/N/R) And still no ENGINE light, so I assume no CODES. True/false? Is a visit to KIA Service my only real choice?

Pull the vacuum line off the fuel psi regulator and have someone rev the engine. Its probably leaking. If it leaks fuel replace it.

OK, now that fuel filter is back in place, ready to test regulator. Anyone (LMP??) got a pic of it, so I am 100% on target? And, if it does leak, will it leak back on vacumn port side, or where? And is this another KIA only part, or is NAPA going to have it?