idle problems

[mechanic47]

I'm still having problems with my 87 shelby z....It will idle around 1500 rpm's for about 5 to 10 seconds,and then drop to 800 rpms when coming to a stop,the only codes are 15 and 55.....15 is the speed sensor,but the speedo and tach works fine.I unplugged idle control motor and nothing changed.I need some ideas on what to try next ,thanks.....I've cleaned the throttle plates,they are free and the cable isn't sticking,I've also went through the steps on setting the aic motor..help

[NAJ]

You can visually check the connector for damage and check the wiring with a multi-meter for open or shorted wiring but without a scanner there is no way to tell if the LM is actually seeing the VSS signal.

1987 Dodge Daytona L4-135 2.2L SOHC Turbo
Vehicle Level Powertrain Management Computers and Control Systems Testing and Inspection Diagnostic Trouble Code Tests and Associated Procedures Driveability (DR) Tests DR-3A Fault Code 15 Speed Sensor Circuit


DR-3A Fault Code 15 Speed Sensor Circuit
Notes

With diagnostic read-out tool connected to engine harness connector, start engine, then disconnect speed sensor connector.
Place system in Engine Running Test Mode 71.
Connect and disconnect a jumper wire between terminals of speed sensor harness connector.
If display on read-out tool changes, replace speed sensor.
If display on read-out tool does not change, proceed to Test 3 step B. See: DR-3B Speed Sensor Circuit to Logic Module

1987 Dodge Daytona L4-135 2.2L SOHC Turbo
Vehicle Level Powertrain Management Computers and Control Systems Testing and Inspection Diagnostic Trouble Code Tests and Associated Procedures Driveability (DR) Tests DR-3B Speed Sensor Circuit to Logic Module


DR-3B Speed Sensor Circuit to Logic Module
Notes

With diagnostic read-out tool connected to engine harness connector, engine running, speed sensor connector disconnected and system in Engine Running Test Mode 71, connect and disconnect a jumper wire between cavity 25 and cavity 9 of red module connector.
If display on read-out tool changes as you make and break this connection, locate and repair open circuit in wires to speed sensor.
If display on read-out tool does not change as you make and break this connection, replace logic module.
CAUTION: Before replacing the logic module check the terminal of cavity No. 9 of the red connector to make sure it is not crushed causing a poor connection.

[mechanic47]

thanks for the info

[mechanic47]

Well,I put in a new vss,cleared the codes and went driving.........I don't have code 15 anymore,only code 12,and 55,12 because I had the battery unhooked for a couple minutes,but I still have the same idle problem,lol....It stays idles up around 1800 rpm for about 10 seconds when coming to a stop,also after its warmed up you have to presss the gas a little or it won't start,any ideas? theres no cable binding or anything,and other that this problem it runs excellent...thanks

[NAJ]

Start with basics.
Be sure the AIS Pintle and bore are clean and that base idle is correct.
Never unplug the AIS while the controller is moving it or damage to a driver in the controller will occur. Be sure the AIS is stepped in to 0 as outlined in the "sticky"."help with poor idle."
Be sure the PCV system is functioning normally, the PCV valve is a metered vacuum leak that is in the controllers programming for idle control.
Be sure the grommet on the valve cover is not cracked/falling apart and that the PCV hose is tight/secure and not collapsed.
The wrong valve or a restricted valve/system will affect idle control. Chrysler used 4 differant PCV valves in the 80's. The turbo valve is the same as the slant 6 and V-8 valve.
Be sure there are no restrictions in the air intake system.
After that be sure ignition timing is correct.
If you can get a hold of a scanner you can watch AIS steps, they should be 10-15 at idle.
Post back after the above have been checked/corrected.

[mechanic47]

well,i think I have it fixed,the ais was practically new and there were no fault codes referring to it,but i took one off an 88 es automatic turbo car(parts car) and put it on my z,set it ,and its idling down now like it should,and you don't have to press the gas pedal to get it to start after its warmed up now,thanks for the information and the help..........Bill

[mechanic47]

too good to be true.......Car ran great yesterday,idled down great,but this evening,its the same old problem........idling 1800 rpm for 10 seconds then dropping to about 1000 rpm's and hunting a little....arrrgggggg..oh yea...no fault codes

[risen]

The 87 cars are set to have a point at which the car switches from a idle while rolling, to the stopped idle. Basically if the car is above ~5 mph or so, it keeps the idle around 1500 rpms until it sees it the car below that speed. Once it drops below it sets the idle to ~900. I'm not sure if you're still having problems with the vss (maybe a flaky connection and not a bad sensor?), or if you're just frustrated at it's default behavior (which I *loathe*). If your vss is good you can adjust the switch point if you change the calibration, I like to set mine to 15mph or so.

[mechanic47]

Quote:

Originally Posted by risen The 87 cars are set to have a point at which the car switches from a idle while rolling, to the stopped idle. Basically if the car is above ~5 mph or so, it keeps the idle around 1500 rpms until it sees it the car below that speed. Once it drops below it sets the idle to ~900. I'm not sure if you're still having problems with the vss (maybe a flaky connection and not a bad sensor?), or if you're just frustrated at it's default behavior (which I *loathe*). If your vss is good you can adjust the switch point if you change the calibration, I like to set mine to 15mph or so.

my cars keeps the 1500 to 1800 rpm idle for about 10 seconds after I am completely stopped,then drops,its really annoying. The vss is new,i did have code 15 but have no codes since I installed the vss,the ony thing that made a difference was replacing the aic,but it was off a parts car and it was good for a day.I'm considering a new aic to see what happens.How do you recalibrate the vss?thanks

[risen]

I don't know if there is a way to recalibrate the vss, because the sensor sort of acts like a HEP (that's a really rough comparison). It switches on and off based upon wheel speed. Maybe you should double check the wiring to the vss and see if there are any breaks? The easiest way of diagnosing it would probably be to hook a scanner up to the car and see if the mph from the ecu actually match your road speed.

[mechanic47]

Quote:

Originally Posted by risen I don't know if there is a way to recalibrate the vss, because the sensor sort of acts like a HEP (that's a really rough comparison). It switches on and off based upon wheel speed. Maybe you should double check the wiring to the vss and see if there are any breaks? The easiest way of diagnosing it would probably be to hook a scanner up to the car and see if the mph from the ecu actually match your road speed.

I'm gonna check the wiring connectors and grounds this evening,and put in a new aic and go from there,thank you for you help