Hard start and high idle
Thread Starter
Pro
Joined: Dec 2000
Posts: 555
Likes: 2
From: RDU NC
Hard start and high idle
This is becoming more frequent with my 85, and it used to only happen every once in awhile. Now it's happening just about every time I drive it.
Cold start= everything totally normal. Once warmed up, the idle drops to around 600 in D. After driving a bit, I notice the idle in D at a light or whatever goes up to 1100- putting in P or N it spikes to about 1400. Usually when it's idling like this the fan is running even though coolant and oil temp are both normal (under 200). Sometimes the CEL comes on for a minute then goes out: the only stored code is: 15 Coolant Sensor Circuit.
Warm start= sometimes very hard to start, sometimes no prob. When the problem arises and I try to start, it catches then dies. Pumping the gas pedal seems to get it fired up, then the high idle happens. Then if I shift into D or R, it dies. If I keep my foot on the gas it stays running; once I'm driving it seems to drive fine- no stumbling, loss of power, etc.
Any ideas on where to look? I will try to get a scan tomorrow, charging up the ol laptop tonight...
Cold start= everything totally normal. Once warmed up, the idle drops to around 600 in D. After driving a bit, I notice the idle in D at a light or whatever goes up to 1100- putting in P or N it spikes to about 1400. Usually when it's idling like this the fan is running even though coolant and oil temp are both normal (under 200). Sometimes the CEL comes on for a minute then goes out: the only stored code is: 15 Coolant Sensor Circuit.
Warm start= sometimes very hard to start, sometimes no prob. When the problem arises and I try to start, it catches then dies. Pumping the gas pedal seems to get it fired up, then the high idle happens. Then if I shift into D or R, it dies. If I keep my foot on the gas it stays running; once I'm driving it seems to drive fine- no stumbling, loss of power, etc.
Any ideas on where to look? I will try to get a scan tomorrow, charging up the ol laptop tonight...
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Sounds like you have a flaky coolant temperature sensor. Possibly the connection is bad somewhere as well. I'd bet there's an inconsistency between the gauge reading and the reading from the ECM.
Code 15 will make it run pig rich, been there, done that. 
Le Mans Master
Joined: Feb 2005
Posts: 6,475
Likes: 564
From: Clearwater Florida
............... A new coolant temp sensor costs $15 or less ... its the smaller one on the front bottom of the intake manifold ... the larger one is the cold start injector timer .............. high idle stuff is usually due to a vacuum leak ... the brake booster is the most common source ........
Thread Starter
Pro
Joined: Dec 2000
Posts: 555
Likes: 2
From: RDU NC
Coolant sensor replaced (the one in the front of the intake manifold). No problems, but then again they were intermittent to begin with. However, the idle seemed to be a little better, more stable.
I also did a scan on my test drive after the car warmed up. My findings:
Coolant temp from scan was ~ 150F or ~66C. Dash readout was around 180. Both would rise and fall at the same time, just different readouts. This is no different than my scans before today.
Seems like the majority of the time it's running rich, but switches between rich/lean and the BLM and INT readings jump all over the place. (BLM min=108 max=128), (INT min=99 max=155).
I'm trying to figure out this whole scanning thing, so I can see things that aren't normal but what to do about them...
I also did a scan on my test drive after the car warmed up. My findings:
Coolant temp from scan was ~ 150F or ~66C. Dash readout was around 180. Both would rise and fall at the same time, just different readouts. This is no different than my scans before today.
Seems like the majority of the time it's running rich, but switches between rich/lean and the BLM and INT readings jump all over the place. (BLM min=108 max=128), (INT min=99 max=155).
I'm trying to figure out this whole scanning thing, so I can see things that aren't normal but what to do about them...
