The PO had to replace the LH on my '89 GT because it got fried trying to jump start it. He replaced it with an '88 LH and I wanted to make sure the chip was changed correctly. The two chips have these numbers on them, 2287355447 and 2287356486. Does anyone know the correct '89 GT LH chip number? I have the LH open and I thought I'd best check. Thanks!

 

Ask Rich Andrade or John Speake. Either one of them should know, but you are correct to question this as they do use different chips. If needed, I can look up my chip when I get home tonight - but I'm not sure how a 91 GT chip compares.

 

I don't recall the number on the '88 LH chip (didn't write it down) but if you need a GT eprom I have one. I experimented using GT chips both EZK and LH in my '88 S4 but with the auto transmission the GT LH eprom wont hold a high enough idle when in the box is in gear which obviously isn't required in any GT with a std gbox. I now run with the stock S4 LH chip but still have the GT EZK prom installed.

The GT eproms were mapped by John Speake.

 

The ......486 is the correct LH EPROM for your 89GT.

 

John, thanks for confirming the #! Any idea why my GT idles around 1000-1100 rpm? Schocki ran the spanner on it and it dropped it down to 800 but I had to disconnect the battery and I'm back up to 1000-1100 rmp. Drives me crazy.

Andrew, thanks for your willingness to check. I do think the 91 has a different # for some reason.

Malcolm, thanks for the offer of assistance, I may take you up on that depending on what John sayes is my issue with the high idle. I had hoped the PO didn't swap the S4 chip and it was set for an auto in nuetral or something. How much do you want for the chip?

 

Vacuum leak or intake leak. Somehow umetered air is getting in there. Check vacuum lines with a mityVac or similar. If that shoes good, I'd suspect it might be time for an intake R&R.

 

I don't think I have any leaks, I've tested as much as I can but I could be wrong, certainly wouldn't be the first time. If there was a leak would the spanner be able to pull the idle down to 775-800 and hold it there? The idle doesn't hunt, it's just that most times it's steady at 1000 but sometimes it's steady at 1100.

 

I'll add that if you have access to an EPROM reader, Bosch was nice enough to include in the ROM code, the specific code number that is on the label and the associated Porsche LH Part number .... so if you don't have a label or if you suspect that the EPROM may have been reprogrammed you can verify what the code in the EPROM is.

I can confirm that the 2 287 355 447 is the code for an '88 LH (928.618.123.11).

Also, if you have a 1991 5-speed (GT), the code should be 2 287 356 878.

 

If the Spanner will make it get to the correct idle speed, then the LH is OK.

Some cars just seem to need a Spanner or Hammer to get them to idle corectly.

There is interaction between the O2 loop, MAF and ISV system. Too many tolerances going the worng way may it necessary to reset idle with a diagnostic tool.

You may have a slight inlet leak that is messing things up.

 

Thanks to all who responded. I tried the S4 LH chip to see what would happen with my GT. It definately doesn't like it, it doesn't run nearly as well. The idle is still high but running about 100 rmp less than with the GT chip which makes perfectly explainable sense the GT has an idle speed 100 rpm higher than a S4.

 

Good to verify you have the right chip etc.............I'll keep mine then?