Hi,
I have a 1999 volvo s40 2.0 petrol, and it had some issues with a failed MAF and IAC which I got replaced recently. Along with that I replaced the TPS, Engine coolant temp sensor, plug wires, plugs. Immediately after replacing the IAC and MAF and starting, the car kept revving upto about 4000Rpm and coming back down to about 1000+ Rpm. This initial spike kept reducing as the engine heated up (during each consecutive start). Anyway after some searching I saw that a bad ECT sensor could do this, hence the replacement. Now that has stopped, but now the car idles very badly, goes down to as low as 500 with the AC on and goes as high as 1200 before coming down to about 700 suddenly. Also the engine is very reluctant to slow down, basically when driving and shifting gears, the engine sort of "hangs" at whatever rpm I pressed the clutch at. This was not the case before with the failed IAC. The engine would instantly drop rpm when I let go of the throttle to shift gears. It feels "sticky" now. We've read the data stream from the scanner and the throttle isnt sticking (tps returns to 0 instantly, ; Id like to add that i took the car back to the garage as I got another TPS failure code, the tps reading kept oscillating between 5 and 0 degrees with no input from us).

 

Those throttle bodies are notorious for being problems. Your TB itself could be the issue. I thought xemodex did the S40 etb's but I guess not..

Still, being a 1999, it wouldn't hurt to clean your throttle body, both sides of the flapper. I would start with giving it a good cleaning until there is no more soot and go from there.

 

Cleaned it, cleaned the iac too, spotless right now. It idles fine without thr AC now, but immediately drops after AC is turned on. Still hangs on high rpms between gear changes.