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Engine idles too slow, stops when gas pedal released.
Road performance normal, gas mileage normal. However, idles at 600-700 RPM, rather than 1000. Taking foot off accelerator invariably results in stall, i,e, engine stops instead of dropping to idle speed. Cause?
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Is the car equipped with the Automatic Transmission?
If so, read on.
Otherwise skip to the end and answer some questions.
POSSIBLE SCENARIO:
I have observed a condition where my car surges slightly when the torque-converter clutch (TCC) cycles between lock and unlock when driving on an uphill grade.
First some basics and history that will explain why the TCC is used.
Engine, Torque Converter, TCC, and Transmission relationship--
The TCC allows for a solid connection between the engine and transmission which allows the input to the transmission to rotate at the same speed as the engine.
Without a TCC, there is slippage between the engine and automatic transmission. The slippage is greatest at low engine RPM. That is what allows the engine to run with the automatic transmission in gear, like when you first shift into gear or stop at a stop sign. When the throttle pedal is depressed, the engine RPM begins to increase and the torque converter begins to slip less and less the more the engine RPM increases. The car moves. But even at cruising speeds the torque converter slips slightly. Engine RPM is greater than transmission input RPM, which is realized as slight decrease in fuel efficiency.
When acceleration is complete and a constant speed is being maintained, the engine power output is reduced to the point where the TCC can engage and eliminate any slippage between the engine and transmission. If the car has a tachometer the engagement of the TCC can be verified when a slight reduction in engine RPM observed without a corresponding change in vehicle speed.
One method used to test the operation of the TCC is as follows:
Find a flat section of road where it is safe to perform the test.
Reach a steady speed and keep the gas pedal depressed with one foot. While observing the tachometer (or listening for an increase in engine RPM), with the other foot depress the brake pedal enough to activate the break light switch but not enough to engage the brakes. When the brake light switch activates, the TCC receives a signal to disengage. With the gas pedal being held steady, release the brake pedal and the engine RPM should decrease when the TCC engages.
Old cars with Automatic Transmissions did not use a TCC. I believe the TCC was put in use in an attempt to increase fuel economy.
MY EXPERIENCE WITH SIMILAR SYMPTOMS
The condition that causes that issue on my car is this:
- A slight uphill grade increases the load on the engine.
The car tends to gradually slow and it is necessary to depress the gas pedal to maintain speed.
- Depressing the throttle pedal (manually, or automatically with cruise control engaged) signals the torque converter clutch to unlock when the load increases slightly. (A more drastic load increase would signal the Transmission to downshift to a lower gear.) The corresponding increase in engine RPM and output is enough to compensate for the reduction in speed. When the vehicle speed, engine RPM, and throttle position stabilize to the point that the TCC will engage and the engine RPM will reduce in correspondence with TCC engagement. Now, if the road conditions have not changed, power output is not enough to maintain vehicle speed. With the increased load caused by full engagement between engine and transmission, and the cycle (surging) repeats itself until the road conditions change.
Does that help?
If not:
QUESTIONS
Please define the symptoms.
What are the road conditions when the surge occurs? (A slight uphill grade?)
What is the frequency of the surge?
Does the engine power output have a noticeable surge?
Is there a speed change related to the surge?
Does the tachometer move up and down with little or no change in vehicle speed?
Are all instrument indication in the normal range?
What else has changed?
No,only on carburated engines it,idles down to the set point,on yours,it's fuel injected,pushing gas pedal won't kick idle down,should go down after a certain amount of time,does it automatically,If you start and drive a 5 mile ride and stop at a stop sign,it should idle at it's set point if there's no engine problems,which may be.5 to .7 on your tac.When you normally first start,it will idle between 1000 to 1200 rpm's,don't push on gas,let idle say 15 seconds,put in drive and go.
You have a mechanical bind. Disconnect the main linkage and work it all by hand. Everything should be free and slopy. Aerosol carb cleaner will help, but only when the engine is not running.
Do the following:
1. Clean the throttle body from inside.
2. Adjust the spark plugs gap to 1.00 mm.
3. Check fuel pump pressure. (44 Psi - 49 psi)
4. Remove the negative battery terminal for 5 minutes.
5. Connect the battery terminal.
6. Check the engine oil level and coolant level.
NOTE: Before starting the engine shut off all lights and loads for example room light, blower, radio, parking light etc.
7. Start the engine and hold the throttle at 3000 rpm till radiator fan comes on.
8. After the fan comes on release the throttle pedal and let it idle for 10 minutes.
hello from what you explained i take it theres no check engine lights on what it sounds like is a basic increase on your idle screw get somone to help push pedal down underhood look to see where gas cable pulls back when gas pedals appled have them release slowly now watch where it stops against a set screw that is your adjustment rpm range should be somewhere between 750-900 rpm depending on vehicle if this doesnt solve most likely tps sensor{ throttle position sensor} goodluck
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