Another cold start rough idle post.

callahanoffroad · Post by **callahanoffroad** » 18 Feb 2019, 06:09

1994/5 Volvo 850 non turbo, manual transmission.

Okay I'm pulling my hair out here. Car is idling rough at idle when it's cold. Basically I have to start it and rev it for about 30 seconds or else it dies. Once even slightly warm it idles fine. So far I've replaced the following components trying to chase this:

Mass airflow sensor (oem Bosch)
Plugs
Wires (bougicord)
Cap and rotor (oem Bosch)
Vacuum lines are all new
PCV replaced 5000 miles ago

Only thing I can think of next is the idle air control valve. Those things are not cheap either. Is there a proper way to test them? I cleaned mine about this time last year.

Power band is still strong. I have no codes.

I offer my supplications to my Volvo brain trust.

Post by **Chuck W** » 18 Feb 2019, 06:22

Have you checked your ECT sensor and connector?

callahanoffroad · Post by **callahanoffroad** » 18 Feb 2019, 06:38

Chuck W wrote: ↑18 Feb 2019, 06:22 Have you checked your ECT sensor and connector?

No I haven't and I'm not actually sure how to do that

callahanoffroad · Post by **callahanoffroad** » 18 Feb 2019, 07:51

Here's everyone's favorite thing...

A video!

Post by **Chuck W** » 18 Feb 2019, 08:07

The ECT is located in the base of the thermostat housing.

Any corrosion on the connector can cause issues, especially when it gets colder. Might not be your issue, but it's an easy thing to check and rule out.
Mine didn't act up until the temps got really cold and made the car run like crap. I cleaned the pins up a bit and it's been fine since.

callahanoffroad · Post by **callahanoffroad** » 18 Feb 2019, 08:53

Chuck W wrote: ↑18 Feb 2019, 08:07 The ECT is located in the base of the thermostat housing.

Any corrosion on the connector can cause issues, especially when it gets colder. Might not be your issue, but it's an easy thing to check and rule out.
Mine didn't act up until the temps got really cold and made the car run like crap. I cleaned the pins up a bit and it's been fine since.

Sprayed it down with maf cleaner, its now idling a little better. Not perfect but much smoother. That's such a weird thing to cause an issue

Post by **Chuck W** » 18 Feb 2019, 08:58

callahanoffroad wrote: ↑18 Feb 2019, 08:53
Sprayed it down with maf cleaner, its now idling a little better. Not perfect but much smoother. That's such a weird thing to cause an issue

Sprayed the connector down? I'd hit the male pins with some sandpaper, if you didn't do that.

I was surprised about the night/day difference on my car. It acted like it was running on 3 cylinders and wouldn't run for crap, even after all of the "Stage 0" stuff. Cleaned up the connector pins, and *bam*, it was running perfect.

WhatAmIDoing · Post by **WhatAmIDoing** » 18 Feb 2019, 10:09

callahanoffroad wrote: ↑18 Feb 2019, 06:09 1994/5 Volvo 850 non turbo, manual transmission.

Okay I'm pulling my hair out here. Car is idling rough at idle when it's cold. Basically I have to start it and rev it for about 30 seconds or else it dies. Once even slightly warm it idles fine. So far I've replaced the following components trying to chase this:

Mass airflow sensor (oem Bosch)
Plugs
Wires (bougicord)
Cap and rotor (oem Bosch)
Vacuum lines are all new
PCV replaced 5000 miles ago

Only thing I can think of next is the idle air control valve. Those things are not cheap either. Is there a proper way to test them? I cleaned mine about this time last year.

Power band is still strong. I have no codes.

I offer my supplications to my Volvo brain trust.

Two things I have done to fix this problem on my T5 after doing the above, as others have said, clean the ECT pins, and replace the fuel pump relay.