98 2.2 Erratic Idle

My 98 5sfe 2.2L auto has a very bad erratic idle. The head was recently rebuilt with  new timing belt, tensioners, water pump, gaskets, plugs, wires, oil and air filters, coolant, drive belts, and the intake and throttle body were cleaned.
The problem is when coming to a stop the idle starts pulsing between about 600 and 800 rpms. It seems worse when the engine is cold. The only codes occasionally I get are P0300 and P0303 the multiple misfires and the misfire on cylinder 3. If I shift the tranny into neutral it goes away for the most part. When its in drive it shakes the engine, and it feels like the car is trying to move harder than normal. The idle's not as bad in park. The fluid and tranny filter were just changed as well.
The engine doesn't seem to burn any oil and it looks very clean.
Could this be a vacuum problem? Any ideas? Thanks for the help.
 

Since you already replaced plugs and wires I'd start with the other usual suspects - leaking EGR and/or vacuum leak. Also make sure the plug wires are connected properly. I assume this happens with or without A/C on? Cleaning the IAC would not hurt as well.

Pedro thanks for the reply. I checked the egr valve per the instructions in the chilton manual and it checked out fine. When the A/C is on it really bogs down the engine. The wires are connected in the right order. I tried checking all the vacuum lines for cracks or anything that may be leaking and found nothing. How do I go about cleaning the IAC?
Thanks

So do you mean the idle problem is ONLY with A/C running? If so there is a problem with the idle-up circuit.

The idle problem happens all the time, worse when cold and it gets even worse with the A/C running. The A/C almost kills the car when coming to a stop.

quote:

ORIGINAL: MTPolaris How do I go about cleaning the IAC?

 
 
There's a lot of posts on this. Just do a search and you should get all the info you need. Since you had the TB done this problem may relate to timing so I would also get the engine timing checked out. I don't know if you can even adjust the spark timing on a 98 but if you can I would see how far it is adjusted as that may tell you that the mechanical timing was not set accurately. If it's easy to remove the upper timing cover to see the cam timing marks I would the align the crank timing mark to TDC compression and see how the cam marks line up.  

i would check you intake manifold it can be cracked and it is sucking air and misfires...i have an 00 mitsu galant and i had to swap my intake manifold because it was cracked and it idled to high and then it got worse and wouldnt idle at all it would turn off. any how check you "intake manifold" especially where the throttle body connects. Also it can be that whoever messed with the throttle body moved the to tps sensor.