Cant slow it down
Thread Starter
Melting Slicks
Joined: Sep 2006
Posts: 3,194
Likes: 27
From: Monroe Twp, NJ
Cant slow it down
OK here what I did so far with no results on the fast idle. I check according to the FSM the IAC motors and resistance is normal. I cleaned the IAc motors, I checked for juice to the IAC motors and all is good. I replaced the CTS sensor with the two prong type and checked the ground on the sensor and all is good. I checked the TPS sensor according to the FSM and all fuctions are normal both under throttle and off. I rechecked the manifold for leaks with WD40 and no change in idle. Car starts and idles at 2200 RPMs and drops down to 1900 when temp reaches 130. Stays at 1600 to 1900 when temp goes above 180 and stays at that RPM after temp reaches over 200.CHecked all bolts on throttle bodys and all linkage all is tight. WHat have I missed? (1984 with Xram manifold and 85 fuel pump with 8746 ECM) Car ran flawless for 9 months of ownership except for a spratic check engine light code 44 (lean ) and 13 (02 sensor).
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by ps374
Car starts and idles at 2200 RPMs and drops down to 1900 when temp reaches 130. Stays at 1600 to 1900 when temp goes above 180 and stays at that RPM after temp reaches over 200.
Originally Posted by ps374
CHecked all bolts on throttle bodys and all linkage all is tight. WHat have I missed?
RACE ON!!!
Thread Starter
Melting Slicks
Joined: Sep 2006
Posts: 3,194
Likes: 27
From: Monroe Twp, NJ
Nope, I did not test the good CTS I took out (because when I up pluged it the idle slowed down even though the car started to miss). I tested it after I bought the new one and it was good. Pretty bright right. I have not taken off the manifold plate in fear it will be in vain since this is NOT a stock 84 set up but the Xram set up. Its a 3 hour job I'm told to get the Xram off. Since I'm extra careful and label EVERYTHING its 4 to 5 for me.I have sprayed every place I could to find a leak if there is one.Other than the fast idle the car runs fantastic, no misses, pulls strong?? If I'm loosing all that vacuum wouldn't the car run crappy? Only code I ever get with this car is 44 lean and 13 02 sensor and that has been spratic since I have owned it these past 9 months. It has a 8746 ECM not the stock set up if that means anything?
Instructor
Joined: Jul 2007
Posts: 229
Likes: 0
From: FT Lauterdale Florida
this is probably a dumb question, but do you think a blade could be hung open partly on one of your throttle boddies? causing a fast idol ?
and could a worn throttle boddie be so badly worn it would cause that much extra air to pass thru it and make the computer add fuel to compensate for lean cond, even when there is no throttle imput thus causing a higher than normal idol speed?
just an idea - probly not the case tho.
and could a worn throttle boddie be so badly worn it would cause that much extra air to pass thru it and make the computer add fuel to compensate for lean cond, even when there is no throttle imput thus causing a higher than normal idol speed?
just an idea - probly not the case tho.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
code
getting a lean code means you have a vacuum leak or a bad oxygen sensor. but I'm with Brian, are you sure you don't have a throttle body cable going bad and keeping one of the throttle bodies open? That is probably the only way it will run that good, and keep those RPM's. by the way, don't put it in drive when it's running like that unless it's pointed AWAY from your other car and your house
Last edited by coupeguy2001; Aug 25, 2007 at 07:50 PM.
Thread Starter
Melting Slicks
Joined: Sep 2006
Posts: 3,194
Likes: 27
From: Monroe Twp, NJ
getting a lean code means you have a vacuum leak or a bad oxygen sensor. but I'm with Brian, are you sure you don't have a throttle body cable going bad and keeping one of the throttle bodies open? That is probably the only way it will run that good, and keep those RPM's. by the way, don't put it in drive when it's running like that unless it's pointed AWAY from your other car and your house
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
On older TPI's you can adjust the position of the TPS sensor to a degree to compensate for high or lower idle conditions. Min is .45V - Max is .63Volts. What does your TPS voltage read in the closed position?
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Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
There is a leak of some type if it is that high. Get a piece of hose and use it to listen for sucking noises on and around the intake.
Thread Starter
Melting Slicks
Joined: Sep 2006
Posts: 3,194
Likes: 27
From: Monroe Twp, NJ
Thread Starter
Melting Slicks
Joined: Sep 2006
Posts: 3,194
Likes: 27
From: Monroe Twp, NJ
Did that many times, I think the neighbors must think I lost my mind running around the motor with a 3 ft length of heater hose to my ear.The only thing Im finding is a slight whistle near the center of the intake and its NOT a sucking sound but a slight whistle.Sprayed it with WD 40 all over the area were I think I hear it with not even the slightest change is RPMs.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by ps374
Nope, I did not test the good CTS I took out (because when I up pluged it the idle slowed down even though the car started to miss).
It has a 8746 ECM not the stock set up if that means anything?
It has a 8746 ECM not the stock set up if that means anything?
Maybe there is something "up pluged" in your ECM conversion.
RACE ON!!!
Thread Starter
Melting Slicks
Joined: Sep 2006
Posts: 3,194
Likes: 27
From: Monroe Twp, NJ
When you unplugged the ECT sensor, the ECM should have seen that as an engine with coolant at -40°. The ECM should have richened the mixture and raised the idle to the highest possible cold idle. Even with a massive vacuum leak, that It should not have lowered the idle speed.
Maybe there is something "up pluged" in your ECM conversion.
RACE ON!!!
Maybe there is something "up pluged" in your ECM conversion.
RACE ON!!!
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
When you first started it up cold, unhooked, it was probably so rich (-40° F) that it couldn't idle as fast as should have, given all the air it was getting. When you plugged the ECT back in, the mixture leaned to something appropriate for the conditions, and the idle went back up. It also makes sense that there were no changes when you unplugged the ECT when warm. That would lead one to believe the ECT and the ECM are working properly. As a further confirmation, you could close the IACs, and for insurance block the idle air passages, and make note of the idle speed. My guess is that it will still idle at 1700 rpms, reinforcing my long distance diagnosis of a vacuum leak.
RACE ON!!!
RACE ON!!!
Thread Starter
Melting Slicks
Joined: Sep 2006
Posts: 3,194
Likes: 27
From: Monroe Twp, NJ
When you first started it up cold, unhooked, it was probably so rich (-40° F) that it couldn't idle as fast as should have, given all the air it was getting. When you plugged the ECT back in, the mixture leaned to something appropriate for the conditions, and the idle went back up. It also makes sense that there were no changes when you unplugged the ECT when warm. That would lead one to believe the ECT and the ECM are working properly. As a further confirmation, you could close the IACs, and for insurance block the idle air passages, and make note of the idle speed. My guess is that it will still idle at 1700 rpms, reinforcing my long distance diagnosis of a vacuum leak.
RACE ON!!!
RACE ON!!!
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
throttle bodies
if the throttle bodies are closed, you are getting air from another source. plain and simple. engines can't raise the rpm without air.
On the early bosch systems, like volkswagen and porsche, they have a cold start valve that only adds air, and the computer / oxygen sensor compensates for the added air by adding fuel. hence, cold operation...add the air, it will feed the injectors.
On the early bosch systems, like volkswagen and porsche, they have a cold start valve that only adds air, and the computer / oxygen sensor compensates for the added air by adding fuel. hence, cold operation...add the air, it will feed the injectors.
4th Gear
Joined: Dec 2008
Posts: 4
Likes: 0
From: St. Louis MO
ECU resets idle
I had this same problem. after I replaced the manifold gasket to solve a coolant leak, the idle was now at 2000 rpm. eventually, I read in my Haynes (I know...) manual that, after replacing or re-assembling the IAC, Idle Air Control valve, the ECU resets the idle speed the first time the car hits 35 mph. I slammed the car into gear and drove it up past 35. It did reset the idle down to about 700 rpm and its working fine now. 1984 C4 crossfire all stock. hope this helps someone.
Last edited by jhhegarty; May 23, 2009 at 09:24 PM.