940 Rough Idle, Stalls in Drive and Reverse

danielclynn · Post by **danielclynn** » 02 Sep 2011, 17:30

1. 1993 940 Non-Turbo Wagon
2. Around 201,000 miles
3.Newish engine put in by horrible mechanic recommended by my uncle (took them over a month). Since then, I've cleaned the IAC valve, MAF sensor, throttle intake, and throttle body. I also replace the hose running from the IAC to the intake, as there was a large tear in it.
4. Los Angeles, CA car purchased in Indiana.
5. Started out as a rough idle the day I got it back from the shop. The mechanic said it was just the new engine settling in. It only got worse. I took a look under the hood and realized the IAC valve was not connected, so I hooked it up. RPMs went from jumping around between 0 and 700 to being fairly steady, but at 1500-2000. I had to apply the breaks really hard to get it to stop, so I figured whatever the problem is, the IAC should be disengaged until it's fixed. I don't believe it is that IAC valve and there aren't any other torn hoses. I looked on many other threads, but it doesn't seem like any of them posted what there solution was.

Here's a video of the rpm, so you can see exactly what it's doing:

Post by **phils94850** » 04 Sep 2011, 11:38

Daniel, welcome to MVS !

Since you stated that you have to push hard on the brakes to make it stop sounds like you have a bad vacuum leak, possibly the brake booster. Its normal for the rpm's to drop in gear compared to nuetral since your putting the engine under a load. Has the engine had all new tune up stuff such as plugs, wires, etc. ?

danielclynn · Post by **danielclynn** » 04 Sep 2011, 13:23

Right on! The brake booster hose looks horrendous. I'll replace it this week and get back to you all.

It has new plugs and wires, although by the looks of it, the mechanic who had my car for over a month put cheap, generic-looking plugs in. There are also spare connectors all over the place not hooked up to anything.

danielclynn · Post by **danielclynn** » 05 Sep 2011, 19:26

Replaced the vacuum hose for the brake booster. No difference. I removed the removed the cruise control cable from the throttle pulley, as my cruise control has never worked anyway. It seemed to smooth it out a little. I then realized that a vacuum hose from from the cruise control servo to the evap valve. Would a leak in the evap system cause rough idle? I'm going look into it and check the PCV system next.

Post by **phils94850** » 06 Sep 2011, 05:04

yes, any type of vac leak will cause a rough idle. Volvos are very picky about the ignition parts. I would make sure you use bougicord plug wires and bosch copper plugs only ! Make sure the plugs are gapped correctly also.

danielclynn · Post by **danielclynn** » 14 Sep 2011, 00:42

It seems like there is a sensor missing. On the passenger side of the engine block toward the rear there is a spot for a sensor, but nothing in it (just beneath the exhaust manifold). Any idea what that sensor would be?

Post by **phils94850** » 14 Sep 2011, 15:21

can u post a pic of the area your talking about ?

danielclynn · Post by **danielclynn** » 14 Sep 2011, 20:29

I hope this helps. Really difficult to get down there with a camera.

danielclynn · Post by **danielclynn** » 15 Sep 2011, 15:01

I think I fixed the problem. The PCV valve was really dirty. I replaced the flame trap and engaged the IACV and it seems to be working fine now.

Correction:

Nope, I was wrong. It's not fixed. This is driving me crazy. After cleaning it, it worked great for a few miles, now it's worse than ever. The RPMs jump all over the place, even when I'm driving.