Rich, high idle, odd shifts

ANSWER : Hi there. The fact you able to get the idle speed to drop by tapping the gas pedal, lead me to believe the high idle is due to a sticking accelerator cable. Another possibility could be, a faulty throttle body not allowing the throttle to return to the closed position. Proper diagnoses should be performed to avoid unnecessary repairs. I recommend having your vehicles high idle be diagnosed and repaired by a certified technician, such as one from YourMechanic.

ANSWER : Hi there. This can be caused by the issues that you mentioned or a number of other things. You need to make sure all of the connectors are making good contact. I would then need to know what codes are in the computer to know if this is a circuit issue or not. Most of the time, it is not the circuit but instead a vacuum leak.

If there is a vacuum leak, then the vehicle will act like this and the computer cannot control the idle. Most of the time it is a bad hose or an EGR valve that is stuck open. That is the most common cause for this. I typically remove the EGR to check it to feel the diaphragm on the bottom of it to see if it is moving correctly. If you need to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose and repair your car’s idling issue.

ANSWER : If the truck runs normal at idle with the iac unplugged this would suggest you have a bad O2 sensor especially if you’ve confirmed the same running condition with two different iac sensors. I would recommend having a mechanic from YourMechanic come to your home to hook the truck up to a scanner to confirm this is the case before replacing additional parts that may not be needed.

ANSWER : Hi There,
What you are describing sounds like possibly a bad speed sensor or potentially a faulty transmission control module, which also controls the speed sensors. The transmission control module has various sensors such as vehicle speed sensors, wheel speed sensors, throttle position sensors, turbine speed sensor, and transmission fluid temperature sensors that all direct information to it in order for it to perform it’s function. Other functions controlled by the TCM are components such as a kick down switch, traction control system, and cruise control module. Any of these may also affect the way the transmission control module performs and controls the transmission and the shifting of your vehicle. A faulty transmission control module may cause also cause a delay in acceleration or erratic shifting of gears. Lastly, this may also be a result of low transmission fluid. I would suggest having a professional from Your Mechanic come to your location to properly diagnose your transmission problem.

ANSWER : Hi there. The engine has a vacuum leak and is causing the engine to stumble down on the idle. Check all of the vacuum hoses and the brake booster for any leaks. The engine is rich for it’s not burning all of the fuel properly and may also have bad spark plugs. If you need further assistance with engine not adjusting the idle, then seek out a professional, such as one from Your Mechanic, to help you.

ANSWER : Hello – there are several problems which could cause the behavior you mention. A failed throttle position sensor can cause the high idle, and poor shift/no shift behavior you describe since the engine & transmission communicate with each other over how much the gas pedal is depressed. Any problem codes that are set (whether the Check Engine is illuminated or not) are valuable for diagnosis – most auto parts stores will read these for free for you. I would recommend having a car is hard to shift completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.

ANSWER : Hi There,
As you may know, after replacing the injection system your car needs to go through a "re-learning" process to bring the idle back down. When the idle is high, when shifting into gear, you may notice a rough shifting reaction due to the fact that the transmission control module receives information from the main computer of the vehicle which also indicates RPM’s and many other things.

Try doing the following which should bring the idle back down to a normal operating level:

1) Start the engine and let it idle in park for 3 minutes. During that period the idle may be higher idle than normal.
2) After 3 minutes, turn the engine off and leave it off for 60- seconds.
3) Start the engine again and let it idle in park for 3 minutes one more time. During these run periods you may see a check engine light. Scan for codes and if you get throttle body related codes, clear them.
4) If the idle speed is still off, drive the vehicle at speeds above 45-mph and operate several acceleration and deceleration cycles. Then repeat step #3 one last time.

This should bring your idle back down to normal. Should you need further help with this, please reach out to us here at YourMechanic as we are always here to help.

ANSWER : Hello. There are a lot of reasons that would cause a high idle, but most of the time it is caused by a vacuum leak. When there is an excessive amount of air entering the engine the computer will compensate with more fuel causing a higher idle. Most of the time the issue is in the intake manifold gasket. I would typically start by checking the engine sensor readings with a scan tool and then check for vacuum leaks with either propane enrichment or by performing a smoke test. If you need to have this idle issue repaired, consider YourMechanic, as a certified mechanic can come to you to [diagnose this high idle problem] https://www.yourmechanic.com/services/engine-idle-speed-is-high-inspection