1995 940 Turbo Won't Idle with MAF connected

Gnarledbark · Post by **Gnarledbark** » 01 Jun 2015, 10:22

So, this sounds pretty simple, like it should be the MAF, but I want to be sure before I invest in yet another part.

Story goes like this, driving along the freeway and suddenly feel a small loss of power. Not enough to be scary, but enough to notice. Try flooring it and it hesitates before it picks up. As the drive progresses (100 miles) it does it maybe 7 or 8 times, becoming worse each time.

My initial thought is fuel, so I start simple, new Fuel Pressure Regulator. No go. Remove throttle body and clean. Now it won't idle. I think I could have disconnected a vacuum line, so I remove the intake manifold, replace all vacuum lines, and while I'm at it, the ETC sensor. Replaced fuel pump and fuel filter, thinking that might have been the cause of my initial problem, and credit it as a wear part (190,000 miles). Now it will only idle with MAF disconnected, but will not handle a load. With MAF connected it will idle for about a second and die. If I press on the accelerator, it will rev up and slowly start to decline in revs until it either backfires or stalls.

Also, if I put my hand over the air intake, the air intake hoses will all collapse, but the engine will not die. Thinking a vacuum leak still, I remove the Intake manifold again, and find all hoses properly connected. Is it because it is a turbo the reason it will still idle with no air intake and MAF disconnected?

Sorry if this is a jumble of thoughts, but any help would be appreciated.

harryhendo · Post by **harryhendo** » 09 Jun 2015, 06:49

Have you checked the idle air control valve (IAC)? I'm assuming that a 1995 940T has the Bosch fuel injection, so there is an IAC in line to the air intake to the intake manifold. It is closed at startup to allow more fuel into the engine when cold, then slowly opens to its full extent as the car warms up. It is silver, has two hoses connected to it, as well as an electrical connector. If it is NOT retracting when the car is warmed up, you will have a rough idle and lack of power. You can remove the part, clean it with carb or throttle body cleaner, let it soak in overnight, then replace. This often works to clean out the gunk inside.

Gnarledbark · Post by **Gnarledbark** » 09 Jun 2015, 16:25

Thank you. I did try cleaning the IAC valve, and tested it by applying 12v to it. The motor operates, but does not open or close very much. I am not sure how much it is supposed to move.

lummert · Post by **lummert** » 09 Jun 2015, 18:36

I'm thinking the LH2.4 IAC valve operates by pulse width modulation.

harryhendo · Post by **harryhendo** » 10 Jun 2015, 08:14

The IAC opens up very gradually, so it is not very noticeable. To diagnose, when the car is completely cold (like after sitting overnight), pull the bottom hose to view the opening (should be closed fully), replace the hose, then drive the car until hot, and pull the bottom hose again to view the opening (should be completely open). If this doesn't happen, replace the valve. They are pretty expensive, unfortunately, around $150.

93Regina · Post by **93Regina** » 10 Jun 2015, 21:43

harryhendo wrote:drive the car until hot, and pull the bottom hose again to view

Last I knew, IAC resets when key is switched off....and it operates during driving also.

Gnarledbark · Post by **Gnarledbark** » 13 Jul 2015, 17:51

So, I replaced the MAF sensor, and the car runs much better. It is now able to accelerate and idle. After reprogramming the ECM (idle until warm, 1 minute in N, 1 minute in D, 20-50% throttle to top gear) and driving it for 20 miles, it seems to run much smoother. However, my idle still feels off. According to the tach it is low, starting at 450-500 when cold, and maybe 600 when warm. I believe this is due to a bad IAC. I "may" have stuck a screwdriver I there and tried to jimmy things around when cleaning it.

Also, my ambient thermometer is reading high. I must have knocked it or its cover at some point. But when it is in the mid 70s out, it says its 108.

Seems like my repairs are causing more problems than fixing.

93Regina · Post by **93Regina** » 25 Dec 2015, 12:03

lummert wrote:I'm thinking the LH2.4 IAC valve operates by pulse width modulation.

Correct!

As noted in this post, Rex/Regina uses PWM also. LH 2.4's IAC PWM-operation is explained in this post.

The question is are LH-2.4 and Regina's IAC compatible when wired correctly:

1. Default opening position with key switched on, as seen in this photo, and when pulsed, does opening close down?

93Regina · Post by **93Regina** » 25 Dec 2015, 12:08

harryhendo wrote:(IAC)...It is closed at startup to allow more fuel into the engine when cold

This photo suggests it is open at startup, which if left unplugged, a high idle position would exist.

Post by **benpineapple** » 12 Jan 2016, 09:58

Sounds to me like a sticky IAC. It should move very freely when disconnected. I had similar symptoms, so I pulled it, doused it in TB cleaner, scrubbed it with a toothbrush and q-tips. Did that repeatedly until I couldn't see any more gunk in it. Also couldn't hurt to clean the throttle body while you're at it.

Could be an IAC issue combined with a vacuum problem though.