1985 vette no cold high idle tried everything.
03-11-2018, 08:19 PM
#1
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1985 vette no cold high idle tried everything.
ok so this is an 85 automatic and its not the nicest car but a good customer brought it to me to fix a what we though was going to be a simple no high idle start stall when cold. so when the car is cold after it sits over night it will start and stall until you open the throttle a little keep your foot on it a minute and it will idle. a little low but gets better as it gets warmer.
new iac twice incase it was bad
new ecm cts on front of intake again twice incase it was bad
pulled throttle body and cleaned every passage they're fine
swapped maf with a friends known good one made no difference.
checked for continuity between all engine sensors and ecm all seem good.
checked all power and grounds at ecm all seem good.
swapped ecms with a good used one no difference at all. both have hlh prom
checked tps ad set base idle using proper procedure and set tps to .5v at idle
the issue is that when the car is cold the iac isn't opening. now if I pull the iac out and screw the pintle back manually and stick it back in the intake and plug it in the car will start and as it gets warm the idle comes down as it should but then next morning bam start stall. I am at the point of pulling my hair out.
only sensor I haven't checked is the mat as its under the plenum in a weird spot can that cause this to happen? I mean if its reading as if its an insane warm condition out side could it trip it? help me please this car is possessed and is draining me of every bit of patience I have.
new iac twice incase it was bad
new ecm cts on front of intake again twice incase it was bad
pulled throttle body and cleaned every passage they're fine
swapped maf with a friends known good one made no difference.
checked for continuity between all engine sensors and ecm all seem good.
checked all power and grounds at ecm all seem good.
swapped ecms with a good used one no difference at all. both have hlh prom
checked tps ad set base idle using proper procedure and set tps to .5v at idle
the issue is that when the car is cold the iac isn't opening. now if I pull the iac out and screw the pintle back manually and stick it back in the intake and plug it in the car will start and as it gets warm the idle comes down as it should but then next morning bam start stall. I am at the point of pulling my hair out.
only sensor I haven't checked is the mat as its under the plenum in a weird spot can that cause this to happen? I mean if its reading as if its an insane warm condition out side could it trip it? help me please this car is possessed and is draining me of every bit of patience I have.
03-11-2018, 08:53 PM
#2
which hlh does it have?
hlh3200 is what you want. buy one and swap it in if its not the 3200.
i had very similar problems on my 85 and it took a long time to sort out. For about 50$ and some ptience you can scan the 85 to do things like check on the cts and iat for thier readings. scanning the 85 is totally ineffective for things other than simple sensor reading which in your case would help.
the only way to test the 85 is in "field test mode" and it forces to car to idle at 1000rpm. For most people that makes a scanner in effectual at setting your idle up around 600 with the iac in the right spot.
in your case, scanning the 85 would be good. because the ecm would immediately try to open the iac up get that 1000rpm idle. you mentioned that the iac does not appear to be opening after an overnight slumber.
IF the ecm is capable of opening the ecm in field test mode then you know the iac is working. Now if the iac responds to the field test instruction of "hold 1000rpm" then i think u have issues elsewhere.
now you might just need to open the butterfly a smidge and adjust your tps back down. that might donit, as long as your iac is shown to function while watching it attempt to open up. you will see the counts as it opens.
https://www.eecis.udel.edu/~davis/z28/
hlh3200 is what you want. buy one and swap it in if its not the 3200.
i had very similar problems on my 85 and it took a long time to sort out. For about 50$ and some ptience you can scan the 85 to do things like check on the cts and iat for thier readings. scanning the 85 is totally ineffective for things other than simple sensor reading which in your case would help.
the only way to test the 85 is in "field test mode" and it forces to car to idle at 1000rpm. For most people that makes a scanner in effectual at setting your idle up around 600 with the iac in the right spot.
in your case, scanning the 85 would be good. because the ecm would immediately try to open the iac up get that 1000rpm idle. you mentioned that the iac does not appear to be opening after an overnight slumber.
IF the ecm is capable of opening the ecm in field test mode then you know the iac is working. Now if the iac responds to the field test instruction of "hold 1000rpm" then i think u have issues elsewhere.
now you might just need to open the butterfly a smidge and adjust your tps back down. that might donit, as long as your iac is shown to function while watching it attempt to open up. you will see the counts as it opens.
https://www.eecis.udel.edu/~davis/z28/
03-12-2018, 09:26 AM
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ok just got to the car this morning its a whopping 28 degrees out. I got the car started with my foot on the gas and then jumped the connector its flashing like mad. so its in closed loop. its 28 degrees out how the hell is that possible. whats is putting this car in closed loop before its warm.
03-12-2018, 09:39 AM
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and if I jump the connectors and start the car the car holds 1000 rpm so like I said iac and wiring is good now why the hell doesn't it work when its supposed to. I think we have a start but where do I go next.
03-12-2018, 09:40 AM
#7
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tunerpro rt
you will need somebody who is computer savvy.
I am not sure what you are referring to when you say you jumped something and something is flashing like crazy. I'm not sure how that tells you the car is it closed loop but it may be that I just haven't come across this before with the early C4's
are you talking about the service engine light and it blinks?
tunerpro rt
you will need somebody who is computer savvy.
I am not sure what you are referring to when you say you jumped something and something is flashing like crazy. I'm not sure how that tells you the car is it closed loop but it may be that I just haven't come across this before with the early C4's
are you talking about the service engine light and it blinks?
03-12-2018, 09:42 AM
#8
it sounds like you might be a mechanic shop owner, before buying the AL DL cable and loading tuner pro RT onto your computer and you should check and see if there are any handheld scanners that will work for the 85.
The handheld scanner might cost of a tiny bit more but it might make it a lot easier for you.
The handheld scanner might cost of a tiny bit more but it might make it a lot easier for you.
03-12-2018, 09:45 AM
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yes a mechanic not a shop owner though just doing this job on the side to help a friend/customer. and yes I read when you ground the diagnostic depending on how fast the ses light flashes it tells you if the car is in open or closed loop. something like if it flashes once a second its open loop and 2.5 times a second its closed.
03-12-2018, 09:47 AM
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and I am not buying a scanner just for this job. I rarely work on these cars i try to focus on anything pre 70s. so there must be a way around a scanner. why would the car be in closed loop?
03-12-2018, 09:49 AM
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ok scratch that I had it backwards the computer is in open loop as it should be and the iac is working because the car will go into hold 1k mode so back to square one what the hell is wrong with it?
03-12-2018, 10:43 AM
#12
OK, that's good information that you can get it to hold 1000 RPM.Can you verify that you followed the minimum idle set procedure?
set the idle for about 550 using the minimum idol procedure. Do you regional man you'll says to set at 450. They later came out with an update to 500. And then again to 550. You should verify that you have the HLH3200.
i'm on the few other things that are all very good, the HLH3200 instructs the car to maintain a higher idol. It is way way way way better.
---
I do not want to open a second can of worms until the minimum idol set procedure And HLH3200 has been installed. But next I would say get out your fuel pressure tester and do a leak down test to see if you have a leaking injectors. Does the exhaust smell Rich? through a series of clamping the hoses back at the tank, you can pinpoint which part of your fuel system is leaking fuel, if it is.Honestly I would set the minimum idol higher first. See if that fixes it.
set the idle for about 550 using the minimum idol procedure. Do you regional man you'll says to set at 450. They later came out with an update to 500. And then again to 550. You should verify that you have the HLH3200.
i'm on the few other things that are all very good, the HLH3200 instructs the car to maintain a higher idol. It is way way way way better.
---
I do not want to open a second can of worms until the minimum idol set procedure And HLH3200 has been installed. But next I would say get out your fuel pressure tester and do a leak down test to see if you have a leaking injectors. Does the exhaust smell Rich? through a series of clamping the hoses back at the tank, you can pinpoint which part of your fuel system is leaking fuel, if it is.Honestly I would set the minimum idol higher first. See if that fixes it.
03-12-2018, 10:44 AM
#13
apologies for the weird verbiage. I am using Siri to dictate these as I am driving and I cannot edit them. Hopefully you can understand!
03-12-2018, 11:40 AM
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no worries about the wording I got through it. ok so here it is point blank and simple its NOT fuel. sorry to be so direct but the issue is that the car is not commanding the iac to open on its own when cold. like I said I can get the car to start and run fine if I just rest my foot on the pedal to open it a hair. so like I said its not fuel or fuel pressure related this is strictly and electrical issue and I have done the minimum idle thing a few times raising it a hair and I have played with it all over and no matter where i put it still no start when cold without cracking the throttle blades open. right now its set so when the car is fully warmed up I have about a 600rpm in gear and 800 in neutral that's as high as I would want it. as for the hlh 3200 I don't think that's my issue either as I have had 2 different computers with 2 different proms and neither made a difference. I understand that the 3200 has a higher base idle but the fact is that the car in the morning is trying to start on an iac in the position it would be in if the car was fully warmed up and I do not know why it isn't getting the command to re open
03-12-2018, 12:32 PM
#15
Cold start injector?
03-12-2018, 12:34 PM
#16
I am leaning that way
03-15-2018, 03:46 AM
#19
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I don´t think it is electrical. Are you sure, that your problem is not related to a vaccum leak. These can be tricky to sort out. You could even have one in the master brake cylinder.
03-15-2018, 09:14 AM
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no its not vacuum everything has been check including the intake runners. the issue is that the iac isn't being commanded to open. even if I go to the car first thing in the morning and pull the iac out before I have even started the car and plug it in and then turn the key on the iac doesn't move in any direction. I kind of get a slight twitch from the pintle and that's it.but if I screw the pintle in and then put it back and start the car cold its fine idle comes up to 1k-1200 and slowly comes down as the car warms up it just never returns once the car sits over night.