Revs dropping in two steps

[olejovky]

Hi folks, a question considering strange reaction after letting off the gas pedal (and after the whole engine being rebuilt, true). So, once you let go the gas, revs tend to stay one or two seconds on the level reached, then they begin to drop normally, but rest another 2 seconds at 1200rpm, after which they finally drop to idle. I checked for air leaks finding nothing, exhaust seems tight, butterfly in the inlet goes fine. I passed through the emission inspection, yet they were unable to communicate with the engine brain, whatever is the correct word to call it. Any suggestions? Cheers Jan

[Chris Tideswell]

It sounds like the throttle cable could be sticking, not uncommon – if this is the issue I would replace the cable instead of trying to lubricate it.

The other through is that the throttle position sensor needs to be reset.

The following procedure has been on many forums and seems to work:

“Start engine and warm engine to its normal operating temperature

Now turn off the ignition.

Switch on the ignition to position II without starting the engine (all the pre-start warning lights ought to be illuminated)

Depress the throttle pedal to the carpet and fully release inside a period of 30 seconds or so.

Wait for about 15 seconds...
Switch off the ignition”

[Rob Bell]

The other possibility is a sticking idle air control valve (IACV). It's function is to control idle speeds, but will also control the rate at which engine speed drops when stepping off the accelerator pedal.

An IACV fault would usually result in a high idle as well though.

[talkingcars]

“Start engine and warm engine to its normal operating temperature

Now turn off the ignition.

Switch on the ignition to position II without starting the engine (all the pre-start warning lights ought to be illuminated)

Depress the throttle pedal to the carpet and fully release inside a period of 30 seconds or so.

Wait for about 15 seconds...
Switch off the ignition”

Almost - Fully and firmly depress the gas peddle FIVE times within 30 seconds.