My coupe won't idle...
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
My coupe won't idle...
and the EGR valve won't hold vacuum.
Are they related?
Thoughts? Opinions? Rants?
Stats: 1985 Stock L98, idle recently got very bad, very fast. Will run and drive, and idle only if I hold the gas- otherwise it will stall out. Also hesitates. Doesn't miss, TPS is .51, FP is 38psi on priming and holds for an hour. Timing at 6*. Battery shows 12V charge, and Alt runs at 14.7 on startup. My FSM leads me to the EGR as the culprit, but I wanted to get the Forums' thoughts.
Are they related?
Thoughts? Opinions? Rants?
Stats: 1985 Stock L98, idle recently got very bad, very fast. Will run and drive, and idle only if I hold the gas- otherwise it will stall out. Also hesitates. Doesn't miss, TPS is .51, FP is 38psi on priming and holds for an hour. Timing at 6*. Battery shows 12V charge, and Alt runs at 14.7 on startup. My FSM leads me to the EGR as the culprit, but I wanted to get the Forums' thoughts.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Mikey, there should be no EGR in park or neutral. But you should be able to get 10" vacumn, on an 87 the vac. should hold for at least 20 seconds. Have you tried plugging off the vac. line to the EGR and see if things improved?
I don't get this part " also hesitates. Doesn't miss".
I don't get this part " also hesitates. Doesn't miss".
Last edited by rick lambert; Oct 29, 2006 at 12:47 PM.
Racer
Joined: Jun 2006
Posts: 408
Likes: 0
From: Elkton MD
Leaky EGR
An EGR that won't hold vacuum causes two problems. A little leak in the vacuum control line. And an intermittent (sometimes huge) problem in the recirculation line. If the valve sticks open wide enough, the car won't start and will idle roughly at best. Highway driving might not be affected much.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
[/QUOTE=mikey whipreck]My coupe won't idle... [/QUOTE]Cut the roof off. Maybe it will idle as a convertible.
The EGR valve is opened by vacuum. The ECM does not supply any vacuum to the EGR valve to open it at idle, as the EGR is to remain closed at idle. Therefore, an EGR valve with a bad diaphragm (it won't open) couldn't be the cause of the bad idle or the hesitation, when it shouldn't be open anyhow. IF the EGR is stuck open, unrelated to whether it holds a vacuum, or not, THAT could be the cause of of the idle and hesitation problems.
RACE ON!!!
The EGR valve is opened by vacuum. The ECM does not supply any vacuum to the EGR valve to open it at idle, as the EGR is to remain closed at idle. Therefore, an EGR valve with a bad diaphragm (it won't open) couldn't be the cause of the bad idle or the hesitation, when it shouldn't be open anyhow. IF the EGR is stuck open, unrelated to whether it holds a vacuum, or not, THAT could be the cause of of the idle and hesitation problems.
RACE ON!!!
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
mikey, I would like to help though I don't think the EGR is the problem. So, basically you have to hold the throttle plates open a little for it to idle correctly?
I'm sure you know these, but I will list anyways. Check /clean the IAC and TB. I'm not certain if the TPS voltage is different but maybe move the voltage up. Have you set the minimal idle yet? The base idle is in the chip. Have you ohmed the CTS in the intake manifold?
Lots of questions, but trying to get a little more info.
I'm sure you know these, but I will list anyways. Check /clean the IAC and TB. I'm not certain if the TPS voltage is different but maybe move the voltage up. Have you set the minimal idle yet? The base idle is in the chip. Have you ohmed the CTS in the intake manifold?
Lots of questions, but trying to get a little more info.
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Originally Posted by rick lambert
I don't get this part " also hesitates. Doesn't miss".
Originally Posted by RRT vette
mikey, I would like to help though I don't think the EGR is the problem. So, basically you have to hold the throttle plates open a little for it to idle correctly?
Originally Posted by RRT vette
I'm sure you know these, but I will list anyways. Check /clean the IAC and TB. I'm not certain if the TPS voltage is different but maybe move the voltage up. Have you set the minimal idle yet? The base idle is in the chip. Have you ohmed the CTS in the intake manifold?
I have never ohmed the CTS, I can give that a shot.
I was led to the EGR because a number of engine people I talked to locally said I was perfectly describing an EGR problem, CFI-EFI indicated I may be experiencing the issue and IRAraid described it perfectly.
Originally Posted by IRAraid
An EGR that won't hold vacuum causes two problems. A little leak in the vacuum control line. And an intermittent (sometimes huge) problem in the recirculation line. If the valve sticks open wide enough, the car won't start and will idle roughly at best. Highway driving might not be affected much.
Thanks for the ideas.
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Racer
Joined: May 2006
Posts: 281
Likes: 0
From: Urbana OH
I am currently having the same problem. For some reason it won't hold an idle to save it's life and I'm sorry but I was an import guy so I know the ins and outs of a small motor but these v-8's got me stumped. My problem started when I went to get it e-checked and I'm wondering if the guy was messing with the electronics enough to mess this up. He also said my timing was just a little off so I'm wondering if that could have anything to do with it.
Thanks for any help you can give me ahead of time. I'm on leave right now so I won't be able to mess with my car until next monday so I'm hoping to get as much info as possible until I go back to Cali and start working on the new baby.
Peace,
Merritt
Thanks for any help you can give me ahead of time. I'm on leave right now so I won't be able to mess with my car until next monday so I'm hoping to get as much info as possible until I go back to Cali and start working on the new baby.
Peace,
Merritt
it helps us all.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by mikey whipreck
Thought I'd finish out this old thread.
I finally got around to replacing the EGR valve- Now my '85 will idle again. That was the problem.
I finally got around to replacing the EGR valve- Now my '85 will idle again. That was the problem.
RACE ON!!!