MAF/Idle Air Control valve 89 740 GL

rybateman · Post by **rybateman** » 19 May 2011, 15:22

Hi guys,

A couple days ago my 89 740 gl ran into some problems. I had noticed a rough idle for the few days leading up to this, and I also noticed that sometimes at stop lights the car would idle dangerously low, sometimes almost to the point that the engine would stall. Finally, while backing out of my driveway the other morning the car died while shifting from reverse to drive and now will not start. The engine will turn over but not start.

After reading a little bit on the forum I've noticed that a lot of people mention the MAF and Idle Air Control valve as frequent problems that could cause some symptoms like this. Does my case seem like an example of those problems?

Secondly, my problem is that I have no clue where these components are located. I was thinking that the MAF should be near/around the air filter, and I was wondering if somebody might be able to clarify for me exactly where it is located. As far as the IAC valve, I have no clue where it is located.

I know that I should have a chilton/haynes manual for the car, which would make it a lot easier to find these parts, but I've looked everywhere in town and have been unable to find a copy. I've got one coming in the mail right now, but I am stuck in a hard spot for the time being without a car to drive.

Also, if you guys can think of anything else that might be causing this issue, that would be great.

Thanks a ton.

rybateman · Post by **rybateman** » 19 May 2011, 16:30

I almost forgot to mention:

Even when I was noticing very rough idle at stop lights, etc., the car was running very well when driving at 10+ mph.

rybateman · Post by **rybateman** » 25 May 2011, 08:31

Update

I went ahead and checked my spark plugs and wires before digging any deeper, but there was no change. Any recommendations? In the meantime, I have gotten ahold of a repair manual for the car, but it seems to be a bit vague on MAF and IAC issues. Can anybody lend a little insight on this? Any other quick checks that I can knock out before going further?

Thanks

Post by **billofdurham** » 25 May 2011, 11:29

Sorry, I missed this when I came back on Sunday.

Have you checked for fault codes using the On-Board Diagnostic (OBD) unit in the engine compartment? This is a first step when diagnosing these cars. Instructions for its use are pinned at the top of the forum.

The locations of the MAF and IAC are in the attached - MAF is #17 in the first diagram and IAC is #1 or #12 in the second.

740 MAF and IAC locations.pdf: (123.33 KiB) Downloaded 1311 times

You can clean the MAF with a spray cleaner which can be bought at most car parts stores. The IAC is a little more difficult as you need to remove it to do the job properly. Do a search in this forum and you will find advice on how to do it.

One major cause of poor idle is a dirty throttle body. It may look clean but if it has been sucking oil fumes for some time it could be in need of a good clean. Again, a search will lead you to help on this.

Look inside the air filter box and you should see a flap that controls the incoming air depending on the outside temperature. When it is cold the flap will close over the air inlet and open another one that draws air over the manifold thereby heating it. As the temperature of the engine rises the flap will close off the hot air inlet and open the normal intake. It is controlled by a thermostat in the flap mechanism and these often fail, usually in the hot air position. Check to see in which position the flap is. If it is stuck open over the manifold it can play havoc with the idle and also make the car run rich.

Bill.