Early 1986 5 speed Idle speed Too High 1200-1400rpm
#16
Rennlist Member
Unlike the S4 the S3 is a cruder ISV and thus are more prone to add a mechanical resistance, then the Driver circuits get over heated and burn out (I think I have 3 LH's now on a shelf with bad ISV drivers), two go directly to ~1,400 RPM, one sometimes works just great, then it creeps up
In both the S4 and the S3 the ISV's are constantly moving, it's not an open or closed thing many fine adjustments, a bench tested unit that opens and closes by adding 12V to one or the other outer two pins (center is ground) won't always function under the load and or heat.
I've installed the after market (BMW) ISV's in two of my own cars and so far they are working just fine, one is in my 86.5 Twin screw, w/o issues.
I'm just saying if all other parts check out (TPS wiring back to the ECU's(not just hearing it "click") etc..) don't rule out an intermittent or failed LH.
As to your question is it the correct power(12v DC) I think it is more of the correct current.
Have you swapped out the LH yet for a know good one?
Dave K
In both the S4 and the S3 the ISV's are constantly moving, it's not an open or closed thing many fine adjustments, a bench tested unit that opens and closes by adding 12V to one or the other outer two pins (center is ground) won't always function under the load and or heat.
I've installed the after market (BMW) ISV's in two of my own cars and so far they are working just fine, one is in my 86.5 Twin screw, w/o issues.
I'm just saying if all other parts check out (TPS wiring back to the ECU's(not just hearing it "click") etc..) don't rule out an intermittent or failed LH.
As to your question is it the correct power(12v DC) I think it is more of the correct current.
Have you swapped out the LH yet for a know good one?
Dave K
#17
Team Owner
I am going to have the computers checked as well as the MAF everything else seems to be working as it should,
and i did find a lot of fouled up things with this intake refresh.
I installed a new Lowe ISV and the idle was able to be lowered via the screw,
then removing the test jumper the idle will sometimes stay low ,
and then after driving it for a few miles it will suddenly go to 1500 or so RPM,
Thats why I am with Dave on this idea of damaged computers
and i did find a lot of fouled up things with this intake refresh.
I installed a new Lowe ISV and the idle was able to be lowered via the screw,
then removing the test jumper the idle will sometimes stay low ,
and then after driving it for a few miles it will suddenly go to 1500 or so RPM,
Thats why I am with Dave on this idea of damaged computers
#18
Rennlist Member
I feel really stupid weighing in on this since I’m no mechanic, but I just had this problem two weeks ago- car was running fine, then on occasion if I accelerated the idle would settle much higher, then I hit the gas and it settles down, then happens again, stays high like at 1800. Sean suggested I disconnect the cruise cable from the throttle and problem solved. I don’t have cruise but I never use it anyway.
#19
Three Wheelin'
I am going to have the computers checked as well as the MAF everything else seems to be working as it should,
and i did find a lot of fouled up things with this intake refresh.
I installed a new Lowe ISV and the idle was able to be lowered via the screw,
then removing the test jumper the idle will sometimes stay low ,
and then after driving it for a few miles it will suddenly go to 1500 or so RPM,
Thats why I am with Dave on this idea of damaged computers
and i did find a lot of fouled up things with this intake refresh.
I installed a new Lowe ISV and the idle was able to be lowered via the screw,
then removing the test jumper the idle will sometimes stay low ,
and then after driving it for a few miles it will suddenly go to 1500 or so RPM,
Thats why I am with Dave on this idea of damaged computers
So unless we've missed something obvious (doubtful), or you guys have other suggestions (we're open to any and all suggestions), then it appears the computers are the next thing to test / repair. Any of you guys know a good LH & EZ computer repair shop? Preferably in the USA?
Thanks for all your help, insight and considerable expertise!
Joel & Mike.
#20
Team Owner
I am going to send these computer to Rich Andrade, he fixed my S4 computers and it was a time consuming issue to effect repair.
Their might be other vendors that will repair these .
Their might be other vendors that will repair these .
#22
Rennlist Member
Joel, I second what Stan said.
I had Rich rebuild the LH 2.2 and EZF for the Red Witch.
I am having him do the same to a spare LH 2.2 and EZF also from an 1986.5 auto, and will have him install the Porken S300 chips in those computers. Rich was not cheap, but was reasonable for the work done.
From what I understand, ALL of the S4 and later LH 2.3 computers WILL fail due to the 'tile' inside. The earlier LH 2.2 computers are a little more robust, but are now suffering from age. Meaning failing solder joints, individual components, etc... Worth spending the money to have them rebuilt now at your leisure instead of later when they are dead.
Also, Stan, to my knowledge, Rich Andrade and John Speake are the only reputable rebuilders of 928 computers. I believe there may be others, but Rich and John have the best reputation and are 'part of the crowd.'
Having said that, if I am wrong, I meant no offense to anyone.
I had Rich rebuild the LH 2.2 and EZF for the Red Witch.
I am having him do the same to a spare LH 2.2 and EZF also from an 1986.5 auto, and will have him install the Porken S300 chips in those computers. Rich was not cheap, but was reasonable for the work done.
From what I understand, ALL of the S4 and later LH 2.3 computers WILL fail due to the 'tile' inside. The earlier LH 2.2 computers are a little more robust, but are now suffering from age. Meaning failing solder joints, individual components, etc... Worth spending the money to have them rebuilt now at your leisure instead of later when they are dead.
Also, Stan, to my knowledge, Rich Andrade and John Speake are the only reputable rebuilders of 928 computers. I believe there may be others, but Rich and John have the best reputation and are 'part of the crowd.'
Having said that, if I am wrong, I meant no offense to anyone.
#23
Rennlist Member
Thread Starter
Seth, Dave and Stan: We're in the process of removing them now. Gonna send both to Andrade... ya know, while your in there Seth, I've changed out the PORKEN 300 chips in my 86.5 every time Ken came out with a new version all the way to the 4.0 chip set. My computer tabs were toast, but I got really good at it, and the car ran like a raped ape... for those of you reading along, that's FAST and it pulled all the way to red line in every damn gear! Very noticeable HP & TQ increase without pinging, etc. You'll need to regap your plugs and get an S4 FPR... those are getting pricey! BTW, If anyone has a spare S4 FPR I'm in the market for one so I can do the same with my 86 (once we get this idle speed resolved).
Thanks again! 928 Buckeye Landsharks RULE!!!!
Joel Roberts
Thanks again! 928 Buckeye Landsharks RULE!!!!
Joel Roberts
#24
Rennlist Member
Mike, I’ve got the latest version of Ken’s chips.
I COULD install them myself. However, since Rich will be in the computers anyway, I’ll let him do it.
I have the new plugs and I have an 88 FPR to match up with Greg Brown’s fuel lines.
I am VERY much looking forward to running the Red Witch with the S300 chips. It is my understanding that a well sorted S3 with the S300 chips is wicked fun. 😈
Good Luck with your computers!
I COULD install them myself. However, since Rich will be in the computers anyway, I’ll let him do it.
I have the new plugs and I have an 88 FPR to match up with Greg Brown’s fuel lines.
I am VERY much looking forward to running the Red Witch with the S300 chips. It is my understanding that a well sorted S3 with the S300 chips is wicked fun. 😈
Good Luck with your computers!
#26
Team Owner
Well I will give Rich a call and discuss this with him .
#27
Rennlist Member
I am VERY much looking forward to running the Red Witch with the S300 chips. It is my understanding that a well sorted S3 with the S300 chips is wicked fun.
Yes it most certainly is!
Yes it most certainly is!
#28
Team Owner
I spoke to Rich tonight and he is interested in checking this out ,
I am going to send him my computers the MAF and the ISV thats made by Lowe.
When I find out the diagnosis,
I will update this thread and maybe Rich will also check in here as I advised him of this thread.
I am going to send him my computers the MAF and the ISV thats made by Lowe.
When I find out the diagnosis,
I will update this thread and maybe Rich will also check in here as I advised him of this thread.
#29
Rennlist Member
Thread Starter
I spoke to Rich tonight and he is interested in checking this out ,
I am going to send him my computers the MAF and the ISV thats made by Lowe.
When I find out the diagnosis,
I will update this thread and maybe Rich will also check in here as I advised him of this thread.
I am going to send him my computers the MAF and the ISV thats made by Lowe.
When I find out the diagnosis,
I will update this thread and maybe Rich will also check in here as I advised him of this thread.
#30
Addict
Rennlist Member
Rennlist Member
Hello all,
I recently repaired a 25-pin Porsche 928 LH that had an ISV circuit failure for a customer on the east coast.
I will check out this 25-pin LH ISV circuit and advise what I find.
Rich
928 Owners Club Membership Chairman
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed - now in print
1979 928 track beast
I recently repaired a 25-pin Porsche 928 LH that had an ISV circuit failure for a customer on the east coast.
I will check out this 25-pin LH ISV circuit and advise what I find.
Rich
928 Owners Club Membership Chairman
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed - now in print
1979 928 track beast