idle problems solved!

dimeified · 01-14-2008, 05:43 PM

Well, once again i have conquered a new issue of mine. For a while my idle would surge during cold starts and then settle out. I figured it my idle valve was dirty so i took it apart and cleaned it and put it back together. Unfortunately, i must not have put it back together properly, because the next day during a drive, the engine started hunting during warmup. I ordered a new valve, and put it on the car. Same problem. After searching around with a dvm, it turned out that i put my original ICV back together wrong, or when i cleaned it, i got the solenoid wet. The icv shorted and took out a couple of dme transistors with it. Replaced them today, 1.79 each at radio shack.

I decided to check the dme because the new valve would not vibrate with the key on, and i could not hear it, however the center terminal of the connector was feeding the icv 12v. further, the dme connector pins showed the proper ohm load when the new icv was connected. So i figured it had to be the dme.

Now i just need to chase down that pesky ground to the clock, glue my window in the track, and find the damn leak that soaks my driver side carpets!

ianc · 01-15-2008, 03:15 PM

Nice post, but pics of the guts of the DME showing the transistors, with an explanation of how you located and tested them and the part #'s of the replacements would make it much more useful.

ianc

Porsche-O-Phile · Porsche-O-Phile's Garage

Or you could've just chucked that whole mess and put on a rockin' set of carbs.

In all seriousness, that's great to hear you figured it out.

dimeified · 01-15-2008, 03:56 PM

Sorry, i had gotten the info from this link in pelican...
http://66.236.61.177/showthread.php?t=346667&highlight=dme+transistor
Unlike the gentleman who i owe the credit to, i unfortunately had to replace BOTH of the transistors. I had some blown pcb traces as well, which you would read on his link to the S4 forums is common. I was able to pick up the transistor locally at radioshack. Traces i repaired with pieces of a guitar string, since i couldnt find any solid core wire in my house, and stranded would be too hard to work with.

DW SD · 01-15-2008, 04:15 PM

way to go mcgyver!! guitar string, bubble gum and some carb cleaner.

Seriously, cool post!

Doug

rnln · 01-16-2008, 08:06 PM

May I ask how do you know the transister is bad? Do you know how to measure them?

Quote:

Originally Posted by dimeified

Well, once again i have conquered a new issue of mine. For a while my idle would surge during cold starts and then settle out. I figured it my idle valve was dirty so i took it apart and cleaned it and put it back together. Unfortunately, i must not have put it back together properly, because the next day during a drive, the engine started hunting during warmup. I ordered a new valve, and put it on the car. Same problem. After searching around with a dvm, it turned out that i put my original ICV back together wrong, or when i cleaned it, i got the solenoid wet. The icv shorted and took out a couple of dme transistors with it. Replaced them today, 1.79 each at radio shack.

I decided to check the dme because the new valve would not vibrate with the key on, and i could not hear it, however the center terminal of the connector was feeding the icv 12v. further, the dme connector pins showed the proper ohm load when the new icv was connected. So i figured it had to be the dme.

Now i just need to chase down that pesky ground to the clock, glue my window in the track, and find the damn leak that soaks my driver side carpets!

beepbeep · 01-17-2008, 03:26 AM

Quote:

Originally Posted by rnln

May I ask how do you know the transister is bad? Do you know how to measure them?

From the top of my head, it should have around 3.3k between C-B and E-B in one direction. If any of pins is "shorted", it's dead.

dimeified · 01-17-2008, 08:29 PM

I didnt really know if they were dead or not. I just knew the DME was the problem. Reading up in that thread the other gentleman started, i read that blown traces and transistors are the most common icv circuit fault in the dme. So for me, it was a crapshoot, and for $4.00 what the hell, why not just buy 2 transistors, take them home, and see if it works. That or spend $$$ $$$ $$$ on a new dme.

rnln · 10:43 PM

The reason is I had to bite the bullet to get DME twice in the past, and both times it turned out that it were not the problem. They are expensive, and I don't have the surging all the time, only once in a while so I rather be sure before I put the solder ion on the board.
Thank you for the info.