Stumbling on acceleration and "chirping noise"

[Tharin]

Hey all, I just convinced my girlfriend to pick up a '91 240sx SE Super Hicas to compliment my '84 300zx Turbo and it's got a slight stumble on acceleration. It's not too big of a deal but I'd really like to get it fixed. I noticed today that the stumble is also accomanied by a slight power lag and a chirping noise for as long as you hold the accelerator steady. The chirping noise is only noticable with the windows down and no stereo so I didn't pick up on it right away.

The previous owner was baffled by the problem and proceeded to replace all the usuals. The car has a new MAF, O2 Sensor, Plugs, Wires, Fuel Filter, and probably a few other parts. I, on the other hand, don't like to buy anything unless I'm pretty sure it's the problem.

I started out by cleaning the AIV valve, which was amazingly clean like most everything else in the car. This had no effect on the problem so I decided to pull codes even though there was no MIL light on. I pulled a VSS code (the speedo works intermittently but I don't think it's related... but maybe it is) and a Knock Sensor code. I erased the codes and let the car warm up and then proceeded to test the RPMS. You could feel the stumble occasionally in idle up through 4000 RPMS. It might occur above that as well but it's late and the neighbors don't like "hotrodding" around here. It feels like it could be a miss but it's very subtle. I pulled the codes again and got a CAS code.

I'll be checking all the connections on the various sensors and getting voltage readings off the ecu tomorrow but I was wondering if there's anything else I should look at. I'll probably pull the timing cover off and remove the guide while I'm at it. Anything else? Thanks.

Tharin

EDIT: Forgot to note... the problem only occurs after the car has warmed up.

[p00t]

Check connections to the distributor, if you keep getting a CAS code try and borrow one first since they are expensive (unless you get one from a junkyard).

Other common causes of stumbling are TPS incorrectly adjusted (too far advanced) and distributor timing too far advanced.

EDIT: almost forgot, dont forget to set engine at TDC before you remove it, TDC mark is 2nd from the left on crank pulley. When you put the dist back in the rotor should be facing #1 contact. If you look on the dist cap youll see where that spot is. Check this after you insert it too because the rotor will turn alittle when you put the dist in.

[Tharin]

Thanks for the reply p00t. I just finished checking all the connections. I pulled the distributor and manually checked the signals per the fsm. I couldn't get a good reading off of what I'm assuming is the 180 signal but that could just be the flakey multi-meter. It was definitly clicking the spark and injectors though. I've been driving around town a bit and pulled the codes several different times and also got a MAF code once and a TPS code once. The knock sensor code is coming back fairly consistently. I havn't seen the CAS code since it came up the one time. I also got a 21 (no ignition reference pulse) but that was because I was messing with the distributor. I'm pretty sure that the problem is a miss now. I held a piece of paper behind the muffler and you can hear and see the paper get sucked back to the muffler occasionally. I'm going to go out now and check the TPS and, if I can get to it easily, the knock sensor. Any more ideas? Thanks for your help.

[s13sr20chris]

are the plugs, wires, cap, and rotor all new oem?