Rev Hang 1998 C70 T5

[tisho97]

Hey guys! I've had a nagging issue on my 1998 C70 2.3 T5 for quite some time - The idle stands high at 1000-1500 RPM and rev hangs under acceleration.

I get a P0505 code - Idle Air Control System Malfunction.

Things I've found and fixed:

1. Leaky fuel injectors O rings - Changed.
2. Bad coolant temp sensor - Changed with an OEM one.
3. Switched the TPS for a different one - no change
4. Switched the IAC valve for a different one that I also cleaned - no change

Vacuum lines seem fine but have yet to go under a smoke test.

After the repairs mentioned above, the car started running way better and the idle started behaving better, but the issue isn't really fixed as it is still high and rev hangs.

The thermostat also needs a change, but I don't know if that has anything to do with the idle issue at hand.

If you have any suggestions, let me know!

Cheers,
T

[scot850]

Have you checked the accelerator cable. They get dry and can also break strands which can cause them to stick. Also liberally lube the spring assembly at the motor end of the cable and make sure it is not sticking.

Neil.

[tisho97]

Have you checked the accelerator cable. They get dry and can also break strands which can cause them to stick. Also liberally lube the spring assembly at the motor end of the cable and make sure it is not sticking.

Neil.

Hi Neil!

I've already checked the cable and it does not seem to stick, at least when the car is in one place.

Most recently, I did that check when cleaning the throttle body flap and it seemed that the flap closes quite easily when the gas pedal is released.

[scot850]

Just for laughs, start the car, and with the hood open, try to close the throttle flap further to see if the cable is fully home. You can adjust the cable length which will, or should adjust the idle too.

Neil.

[JimBee]

My 850 base had this issue after I had unplugged the throttle position sensor to move its cable while I was changing the starter.
After unplugging the TPS, again, and firmly replugging it, it settled down to around 1K, sometimes dropping to 900, which is where it's pegging. I also put a little dialectric grease on the contacts.

Usually on cold startup, it's around 750 where it should be but then immediately rises to 1k, so I'm still suspecting the TPS is causing the higher revs, but at 1k I'm leaving it there. I think the TPS housing can actually be loosened and rotated a bit, might be worth trying.

[JimBee]

My 850 base had this issue after I had unplugged the throttle position sensor to move its cable while I was changing the starter.
After unplugging the TPS, again, and firmly replugging it, it settled down to around 1K, sometimes dropping to 900, which is where it's pegging. I also put a little dialectric grease on the contacts.

Usually on cold startup, it's around 750 where it should be but then immediately rises to 1k, so I'm still suspecting the TPS is causing the higher revs, but at 1k I'm leaving it there. I think the TPS housing can actually be loosened and rotated a bit, might be worth trying.

[V50M66]

Definitely sounds like a vacuum leak at the intake manifold. Check all TCV lines, vacuum lines to the intake, vacuum tree, and gaskets.