Huge Hesitation problem

[e36'n]

My dad has a 1985 635csi that all of a sudden refuses to rev normally and hesitates from 1500-2200rpms. The airflow sensor seems to be alright and a mechanic checked the resistance in the spark plug wires and they were all okay.

Does anyone know what this could be as it has been a problem from the start?

Thanks in advance

[bumbavfan]

Hey,

My car had a similar problem, and it turned out to be a dirty connector to the TPS. Here's a few simple things to check out, listed in order of probability that it may correct your car's condition:
1. Check the TPS, iddle speed valve and there's another connector on my 88 635csi right under the TPS (not sure what it does). Clean these out with compressed air (from compressor or compressed air cans like for cleaning computers). You may want to spray electronics cleaner in there too. Then plug back in.
2. Check the barrel connector for the Oxygen sensor (where it attaches into wiring harness). The connector is probably black in color. Again, same as above, check to make sure it's clean. You may want unplug and plug a few times to make sure you have clean metal contact on the connectors, do the same for the connectors mentioned above.
3. Check to make sure there are no loose ground wires. There should be one for the engine to chasis (back of the cylinder head, passenger side) and there should be a ground for the battery. There may be more, I'm not that familiar with my car yet.
4. Going back to 1, if you have a bentley manual and a voltmeter, you may want to check out the TPS and the Mass Flow Sensor to make sure all outputs/ resistances are within spec.
5. Check fuel filter, check spark plug gap, check spark plug wires for insulation damage, check rotor for cracks.
6. Going back to 1 again, unplug the idle speed control valve. Rev the engine up. Any change? If this cures the problem, you may be able to clean the valve with carb cleaner or brake cleaner. It's worth a shot. But really, this valve should not affect engine operation at the speed you descrivbed.
7. I don't think this could cause the problem you describe, but the temp sensor can cause a wondering or a rough idle. If the temp sensor is faulty, it sends incorrect info to the computer which also uses this information and info from the Oxygen sensor to set idle conditions. So, short story long, if this sensor has not been replaced, and the above has not worked, you may want to replace it. It's about $25 from Napa.

Good Luck.

[e36'n]

thanks for the help...i will look into this tomorrow....sorry for my ignorance but does tps stand for throttle position sensor?

where is that looked exactly?

[jcsomerset]

THrottle positoin sensor is correct. - omn my M6 it's on the fron of the first throttle body. On the single Throttle body car - look around the throttle body at the head of the intake manifold. - it looks like home plate and should be around the flap valve hinge thingy - or on the firewall - i forget which ....

Gee - I bet that was helpful-