Question about 1999 Saturn SL

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Erratic idle When it?s cold, the car ides fine. But once the car warms up it has a very erratic idle. I have replaced the IACV, TPS, and o2 sensor. Any other suggestions?

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I recently bought a Saturn for my daughter. The car had a hard starting problem (it crank and crank before firing). I got on this site and one possible solution was the temp sensor for the computer. The original unit has a plastic tip that cracks and lets coolant into the electronics. As a temp related problem I would suggest you check or change the temp sensor. At my local Auto Zone the part cost $8.99, so its not an expensive gamble.

Posted on Jul 20, 2010

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My 94 bmw 325i has a idle problem when warm, idles good at start up and when warm after 1st start up, could it be idle control valve and where is iacv located on this car, it only does this on initial...


Why are you convicting the idle control valve? was it properly diagnosed? Could be coolant sensor, intake sensor,O2 sensors etc. Check it out first.

May 03, 2014 | 2007 BMW 3 Series 328i

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1994 chevy c 1500 shuts off everytime i stop


Possible TPS (Throttle Position Sensor) issue. The TPS controls idling speeds under all conditions. Although the truck may idle fine when cold, once warm, if you are encountering sputtering or stalling, the TPS could be the culprit. Other possibilities could be fouled spark plugs,bad wires, or a bad distributor cap.

Mar 04, 2012 | 1994 Chevrolet C1500

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Vehicle has a erratic idle . replaced egr valve,tps and idle air control valve . still have the problem.vehicle has the 2.0 litre engine.could not find any vacuum leaks.


Sounds like the engine may have internal wear, whereby the replacement of the egr valve, tps, and iacv won't solve the problem. Perhaps try to do a compression test to find out if the rings and valves are ok. There could also be a problem with a timing chain being worn if so equipped, which affects timing. Sometimes wear inside the engine can throw it out of specifications that the car was originally built to causing an erratic idle on the 2.0L engine.

Nov 04, 2011 | 2003 Mazda Protege

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I have a 1989 ford bronco with a 302 that ideals up and down and dies out when park in red light


A number of things could be the problem here:
  1. Bad plugs - fouled plugs would cause erratic idling
  2. Bad wires - also would cause erratic idling
  3. Bad or worn distributor cap
  4. Bad MAF (Mass Air Flow) sensor
  5. Bad TPS (Throttle Position Sensor - this controls the idling speed under all conditions. A bad TPS would idle fine under certain conditions ie engine cold, engine warm with AC on etc but could be bad when truck is warm and at a stop.

Oct 10, 2011 | 1989 Ford Bronco

1 Answer

My 1999 caddilac eldorado feels like it wants to stall while in gear


Several conditions could be the cause of your problem.
  1. Bad MAF (Mass Air Flow) sensor - often responsible for erratic idling
  2. Bad TPS (Throttle Position Sensor) - controls idle speed under all conditions ie warm, cold, + with A/C running.
It's possible to diagnose further by getting a diagnostic test done. Most chain auto parts stores will run a free diagnostic test to obtain a OBDII code (these codes specify which components are either failing or not responding) It is possible that a combination of both the MAF and TPS are contributing to your problem. If the car will idle when cold and only wants to stall once warm and under way, it's more likely than not to be the TPS.

Mar 05, 2011 | 1999 Cadillac Eldorado

2 Answers

Idle fluxuates up and down consistantly


Check the Idle Control System

Idle speed is controlled by the Idle Air Control Valve (IACV). The IACV changes the amount of air being bypassed to the intake manifold, in response to electric current controlled by the ECM. When the IACV is activated, the valve opens to maintain proper idle speed.

Symptom and Subsystems to Check:

1. Difficult to start engine, when cold--check Fast Idle Thermo Valve.

2. Fast idle out of spec, when cold:
a. Check Fast Idle Thermo Valve.
b. Check IACV.
c. Check idle adjusting screw (see Section C).

3. Rough idle:
a. Check hoses and connections.
b. Check IACV.

4. RPM too high, when warm:
a. Check IACV.
b. Check Fast Idle Thermo Valve.
c. Check hoses and connections, check Power Steering Pressure Switch Signal, and check idle adjusting screw.

5. RPM too low, when warm:
a. Idle speed is below specified rpm, with no load--check IACV and idle adjusting screw.
b. Idle speed doesn't increase after initial start up--check IACV.
c. Idle speed drops in gear (automatic transmission)--check automatic transaxle gear position switch signal.
d. Idle speed drops when AC is on--check air conditioning signal and IACV.
e. Idle speed drops when steering wheel is turned--check power steering pressure switch signal and IACV.
f. Idle speed fluctuates with electrical load--check hoses and connections, IACV, and Alternator FR Signal.

6. Frequent stalling, while warming up--check IACV and idle adjusting screw.

7. Frequent stalling, after warming up--check idle adjusting screw and IACV.

Additional Steps:

. Check Alternator FR Signal. Have alternator inspected, if idle speed fluctuates with electrical load. The FR signal communicates to the ECM how "hard" the alternator is working to meet the electrical demands of the car, including the battery and any loads which aren't monitored by the ELD. This square-wave signal varies in pulse width, according to the load on the alternator. The ECM places, approximately, 5 reference volts on the wire. The voltage regulator will drop this signal to approximately 1.2 volts, in proportion to alternator load. The ECM compares the electrical load (ELD) signal with the FR (Charging Rate) signal from the alternator and uses that information to set the idle speed and turn the alternator on and off. This helps fuel economy.

. Clean main ECM ground on thermostat housing.

. Reset ECM, by removing the 7.5 amp Back Up Fuse, in the under-hood fuse box, for 10 seconds.

. Replace PCV Valve, cleaning hose with brake cleaner spray.

. Substitute a known-good ECM. If symptom goes away, replace original ECM.

Check the ICM (Erratic RPM and PGM-FI System)

When the engine is cold, the air conditioner compressor is on, the transmission is in gear (automatic transmission only) or the alternator is charging, the ECM controls current to the Idle Air Control (IAC) Valve to maintain correct idle speed. Here's an overview of how the PGM-FI System works.

Background:

Various inputs to the ECM are TDC/CKP/CYP Sensor, MAP Sensor, ECT Sensor, IAT Sensor, TP Sensor, HO2S, VSS, BARO Sensor, EGR Valve Lift Sensor, Starter Signal, Alternator FR Signal, Air Conditioning Signal, Automatic Transmission Shift Position Signal, Battery Voltage (Ignition 1) Brake Switch Signal, PSP Switch Signal, ELD, and VTEC Pressure Switch.

Inputs are received and processed by the ECM's Fuel Injector Timing and Duration, Electronic Idle Control, Other Control Functions, Ignition Timing Control, and ECM Back-up Functions. These are the primary functional areas within the ECM.

Outputs from the ECM control Fuel Injectors, PGM-FI Main Relay (Fuel Pump), MIL (Check Engine Light), Idle Air Control (IAC) Valve, A/C Compressor Clutch Relay, Ignition Control Module (ICM), EVAP Purge Control Solenoid Valve, HO2S Heater, EGR Control Solenoid Valve, Alternator, Lock-up Solenoid Valve A/B (A/T), VTEC Solenoid Valve, and Interlock Control Unit.

Idle RPM:

Once you understand how the PGM-FI system is configured, it's easy to see how the ECM, Idle Air Control Valve, and the Ignition Control Module affect idle rpm. If the ECM's Electronic Idle Control function is not working properly, then it cannot properly control the IAC Valve. Likewise, if the ECM's Ignition Timing Control function is not operating properly, it cannot properly control the ICM (igniter). Obviously, idle rpm will also be affected if there's a problem with the IAC Valve or the ICM. As stated above, the ECM controls current to the Idle Air Control (IAC) Valve to maintain correct idle speed. This cannot happen if the IAC Valve is failing. The same situation exists if the ICM is failing. The ECM will tell the ICM to open and close the primary voltage circuit going to the coil and it won't respond properly. The result will be erratic spark plug firing and erratic rpm.

Conclusion:

If you are experiencing erratic idle rpm, try and isolate whether the problem is caused by the ICM (ignitor), IAC Valve, or the ECM. My experience has been that a failing ICM is usually responsible for the problem. Keep in mind that tachometers are connected directly to the ICM. Therefore, a fluctuating tachometer needle is often a dead giveaway. Heat and poor preventive maintenance (causing high secondary voltage to be discharge on internal distributor components) frequently causes the ICM (and coil) to fail. Besides performance, this is another reason why it's important to regularly replace spark plugs, spark plug wires, rotors, and distributor caps. Electricity will always follow the path of least resistance, even if it isn't the intended one. Our job is to ensure the intended path is the path of least resistance.

Ignitor (ICM) and Coil Replacement:

1. Disconnect negative battery cable.
2. Remove hex head machine screws, securing distributor cap to housing, using an 8 mm nut driver.
3. Move distributor cap and wires off to the side.
4. Remove machine screw securing rotor to shaft, using a #2 Phillips head screwdriver. It may be necessary to "hit" the starter once or twice, in order to rotate rotor for access to mounting screw.
5. Remove rotor and leak cover.
6. Unfasten ignitor wires, remove coil mounting screws, and set coil aside. Note: Removing coil first improves access to igniter.
7. Unfasten screws securing igniter to housing.
8. Remove ignitor from distributor and unfasten screws mounting ignitor to heat sink.
9. Coat back of new ignitor (or old igniter, if reusing) and male connectors with silicone grease. Silicone grease increases heat transfer to heat sink. Failure to apply silicone grease will cause the ignitor to quickly fail.
10. Mount ignitor to heat sink and reinstall ignitor, igniter terminal wires, coil, coil wires, leak cover, rotor, and distributor cap. Ensure female ignitor terminals fit snugly--crimp with pliers, if necessary.

AutoZone can test ICMs and coils for free. If you plan to keep the car, I would replace the ICM due the age of your Civic.

Sep 15, 2010 | 1991 Honda Civic

2 Answers

1988 mustang rough idle its fine nwhen its cold then when it warms up it gets erratic


check plugs .rotor arm .distibuter cap .or check for dirty fuel filter

Feb 24, 2009 | 1992 Ford Mustang

4 Answers

85 trans am 305 mpfi rough idle at start


check your Temp sensor for the ecu. could be out of spec at lower temps but not enough to send a code "You know -40 is possible and won't send a code"

Nov 11, 2008 | 1985 Pontiac Firebird

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