Symptom-punch throttle in N and revs slow to return to idle

[SSovaiko]

Anyone experienced this? At idle in N, punch the throttle maybe mid-way, the engine races above 2000-2500rpm but takes its sweet time to return to idle (maybe 3-4 secs), much longer than it used to in my 99 24v. Is this common to the 3rd gen common rails?

I don't recall how I discovered this, but it bugs me... . it's been there long before I added any mods to the beast. Thanks!

 

[cerberusiam]

Its normal, in order to keep the spikes in the rail to a minimum the injectors don't just immediately quit injecting. They ramp down when you you just dump the throttle.



If the rpms step down rather than in a smooth curve that usually means there is a problem with injectors or possibly an FCA. The ramp down should be fairly smooth.

 

[SSovaiko]

Wow - that's great news - it does ramp down rather smoothly, but it just takes a few seconds. I had read somewhere that slow return to idle might be a leaky inj symptom, but I see your point - thx for the reply!

 

[cerberusiam]

Wow - that's great news - it does ramp down rather smoothly, but it just takes a few seconds. I had read somewhere that slow return to idle might be a leaky inj symptom, but I see your point - thx for the reply!

A leaky injector usually, not always, shows as a stepped idle down. A bad FCA can add some uneven ramp down also. The more fuel you add with a tuner the longer it will hold at max rpm and the slower it ramps down. Just the nature of a common rail.