What settings do I play with if the revs are not dropping when I left of the gas and I'm still in gear? E.g., I'm driving at 40 mph in 4th, I see a red light so I go off the throttle but the car just continues on at 40 mph or maybe VERY slowly starts to slow down. It's clear that the car is not engine braking like I'm accustomed to.

thanks

 

Sounds like overrun fuel cut?

Does it idle high? If you rev the engine without load, does it linger at higher rpm abnormally long?

 

?

Regardless of over-run, a closed throttle will cause engine braking.

Are you sure that the throttle is not physically binding up? Eg, if you were to drop it into neutral and release the throttle, what would the engine do?

 

I will try neutral tomorrow and see. I did confirm that the TPS was at zero during this (also tried recalibrating TPS). I'll try to get it in a log.

 

A revision to my last:

Regardless of over-run, a closed throttle will cause engine braking, presuming that the IAC valve isn't stuck wide-open (and even then, it's kind of a stretch.)

 

in addition to cutting fuel, you need to cut air, so either one the other or both are not being cut

so like joe said, in addition to checking fuel overrun cut Id look at the iacv

 

At what RPM is that?

 

I want to say it's around 3000. I am about to drive to work. I'll update in abit.

 

Take a datalog if possible, remember to hit spacebar at the exact moment you notice the problem.

 

Will do

 

My money is on the IAC valve. Occasionally my PID stuff whacks-out and decides to idle at the cut-off limit of 3000rpm for a few seconds or longer, then reconsiders and lowers RPM.

Dimitris,
I still owe you some data, maybe tomorrow before the gastro-enterologist.

 

I think the log is too big to attach? The upload keeps failing? Is there a way to chop the log into smaller pieces? For now, screen shots are attached.

The first two markers (earlier on in the log) kind of bracket one of the examples. Looking at the first one, the rpms went from 2563 to about 1500 over 15 seconds. That's a drop of 66 rpms/sec for those keeping score at home. The third marker identified the end of one of the examples. That time the rpms went from 2912 to 2324 over about 10 seconds. That's a drop of 58 rpms/sec. Am I being too critical?

The last marker identifies where the car almost stalled out after coming to a stop with the AC on.

 

I have a feeling your idle settings are fubar. Is your iacvv staying open?

 

How do I determine if it is?

 

Look at the log.

 

I can't find where that is indicated... Do I have to add that parameter to the log? Or is just not called iacvv? I've got a lot to learn...

 

Idle steps or something like that....been a while since I looked at an ms1 log

 

Maybe I'm confused, but this is one of Rev's units that is based on MS2 right?

There is a "PWM Idle Duty" that was holding steady at 25.8 during the first example. For the second example, that value was at 40.2 for the first 5 seconds and dropped to 25.4 for the last five seconds.

 

Maybe I should have pointed out that my car is a normally aspirated '99.

 

Allen send the datalog to my email please.