Extremely Erratic Idle
06-16-2024, 01:26 PM
#1
Cruisin'
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Extremely Erratic Idle
Hello friends, I recently just bought my first car (a 85.5 944) and am looking to solve my idle issue. Upon trying to start I get a couple hard cranks with a pretty consistent start on the third try. Besides the point. When it’s started, my 944 idles either around 1000RPM but will often oscillate between 1k and 3k RPM rapidly. I have a couple suspicions. 1. Being the ICV 2. Some fuel system maybe the Throttle Body. I just bought this car and would like to solve this idle issue before addressing my belts and water pump. The PO said he replaced the vacuums, fuel lines, Distributor rebuilt, regulator, and had the DME rebuilt. The drivetrain is otherwise solid but this looks like my first major project. If anyone can help I’d really appreciate it.
06-16-2024, 04:48 PM
#2
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Vacuum whats replaced?
Remove and inspect the J boot for cracks. Check the ISV hoses and connections for cracks and damage. Sounds like a huge vacuum leak. Find that plastic elbow on the ISV hose that gets cracked or torn.
Try starting with the AFM unplugged if you do not find a big air leak.
The DME relay is not related to this problem but you should make sure you have a newer DME relay from a quality manufacturer (Streibel or the solid state one) relay with the 993 part number and carry a spare or the DME relay jumper.
Remove and inspect the J boot for cracks. Check the ISV hoses and connections for cracks and damage. Sounds like a huge vacuum leak. Find that plastic elbow on the ISV hose that gets cracked or torn.
Try starting with the AFM unplugged if you do not find a big air leak.
The DME relay is not related to this problem but you should make sure you have a newer DME relay from a quality manufacturer (Streibel or the solid state one) relay with the 993 part number and carry a spare or the DME relay jumper.
06-16-2024, 06:09 PM
#3
Cruisin'
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Vacuum lines. Ok I’ll try your suggestions and post what I find.
I guess a better description is it surges on a consistent interval. It has only revved to 3000rpm at idle once. It more often surges at idle.
the PO had this list for me of stuff he did to get it running:
$149 (fuel line) (R)
-$59 (regulator) (R)
-$60 (check valve) (R)
-$170 (tune up) (R)
-$80 (Facets) (R)
-$51 (vac. res.) (R)
-$201 (vac. lines) (R)
-$38 (injector rebuild) (R)
-$20 (wire wheels) (R)
-$20 (drill brushes) (R)
-$24 (iso. bolts) (R)
-$113 (plug wires) (R)
-$115 (coil) (R)
-$146 (ignition switch) (R)
-$524 (DME rebuild) (R)
-$45 (struts)
-$12 (x relay)
I guess a better description is it surges on a consistent interval. It has only revved to 3000rpm at idle once. It more often surges at idle.
the PO had this list for me of stuff he did to get it running:
$149 (fuel line) (R)
-$59 (regulator) (R)
-$60 (check valve) (R)
-$170 (tune up) (R)
-$80 (Facets) (R)
-$51 (vac. res.) (R)
-$201 (vac. lines) (R)
-$38 (injector rebuild) (R)
-$20 (wire wheels) (R)
-$20 (drill brushes) (R)
-$24 (iso. bolts) (R)
-$113 (plug wires) (R)
-$115 (coil) (R)
-$146 (ignition switch) (R)
-$524 (DME rebuild) (R)
-$45 (struts)
-$12 (x relay)
Last edited by henreezy; 06-16-2024 at 06:14 PM. Reason: Updated info
06-21-2024, 11:22 AM
#4
Burning Brakes
welcome henreezy.
Unfortunately you seem to have inherited a car that the PO had no understanding how the Bosch fuel injection and ignition system works and has basically just replaced or fiddled with everything in the vain hope that some thing would suddenly cure the problem. This approach just cost lots of money and unecessary work but worse still....... adjusting and fiddling with settings and components at random increases the number of issues that the car now probably has .
the best thing you can do at this stage is to only change one thing at a time and note down what effect that has if any. If there is no improvement then return the setting or component to its previous state which you hopefully noted or marked.
Post #4 in this thread might be helpful. https://rennlist.com/forums/944-turb...any-ideas.html
Unfortunately you seem to have inherited a car that the PO had no understanding how the Bosch fuel injection and ignition system works and has basically just replaced or fiddled with everything in the vain hope that some thing would suddenly cure the problem. This approach just cost lots of money and unecessary work but worse still....... adjusting and fiddling with settings and components at random increases the number of issues that the car now probably has .
the best thing you can do at this stage is to only change one thing at a time and note down what effect that has if any. If there is no improvement then return the setting or component to its previous state which you hopefully noted or marked.
Post #4 in this thread might be helpful. https://rennlist.com/forums/944-turb...any-ideas.html
06-23-2024, 07:01 PM
#5
Cruisin'
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Hey All, I mistakingly started a new and I now realize this will make the thread confusing. I have taken all the tips previously listed to mind, and will report back with my findings on the new thread. If possible, please disregard this thread in the future. I apologize again!
New Thread
https://rennlist.com/forums/924-931-...rs-needed.html
New Thread
https://rennlist.com/forums/924-931-...rs-needed.html
Last edited by henreezy; 06-23-2024 at 07:03 PM.
06-24-2024, 06:27 AM
#6
Burning Brakes
No worries.....when looking for advice it can be frustrating waiting for a day or two to see a response but we are just owners like yourself and most are probably at work during the day and many other owners around the World won't see your posts for many hours due to time differences
The best way to get your post noticed, if you don't get a prompt response, is to bump your post up to the top of the daily posts.
you can do this by either simply answering other poster's questions or advice, or by posting an update to the thread yourself.
If you wish to stick to the second thread it would be very helpful to other members viewing this thread in the future to go to your first post in this thread and select 'EDIT' then remove your thread title and replace it with the word 'SOLVED' then it will mostly get ignored .
Lastly you haven't responded to my suggestion to look at the forth post in the link that I provided for you. It may not be relevant and it may not be helpful to you but nevertheless you should always reply to suggestions and advice or at least acknowledge it with a thank you.
The best way to get your post noticed, if you don't get a prompt response, is to bump your post up to the top of the daily posts.
you can do this by either simply answering other poster's questions or advice, or by posting an update to the thread yourself.
If you wish to stick to the second thread it would be very helpful to other members viewing this thread in the future to go to your first post in this thread and select 'EDIT' then remove your thread title and replace it with the word 'SOLVED' then it will mostly get ignored .
Lastly you haven't responded to my suggestion to look at the forth post in the link that I provided for you. It may not be relevant and it may not be helpful to you but nevertheless you should always reply to suggestions and advice or at least acknowledge it with a thank you.
