RPM's drop slowly between shifts

[Mysterytrain]

Hey Guys..quick question. What would cause my fresh rebuilt 3.2 short stroke to keep the rpm high between shifts ( actually they slowly drop down when you come off throttle ). Car idles nicely, just kinda hangs the revs between shifts.

[jluetjen]

What sort of induction system are you running? CIS, Carbs or something else?

[echrisconnor]

If the car runs CIS, it's almost certainly your Deceleration valve. The vacuum line to it can be plugged and revs will drop very quickly. Or depending on the year of the system, they're adjustable.

If it's carbs, or motronic, I can't help ya'.


chris

[Mysterytrain]

oops, yep its CIS.

[Grady Clay]

It can also be a vacuum leak. Damaged air box?

Best,
Grady

[Wayne 962]

Stuck or sticky throttle linkage or sensor plate too...

-Wayne

[RoninLB]

Originally posted by echrisconnor
If the car runs CIS, it's almost certainly your Deceleration valve.

happened to me on stock CIS

[Mysterytrain]

Thanks guys I tweeked the decel valve and that seems to have cured that issue..its does a strange thing after it warms up...hangs at 2K once it reaches 180 deg. Starts normal from cold, ck'ed the AAR open when cold /closed when hot. Idles great from cold start to 180 then it hangs..any thoughts.

[RoninLB]

Originally posted by Mysterytrain
..any thoughts.

try disconnecting it. On my system's decel model it was removing the small top control hose and pluging the hose.

[echrisconnor]

Have you checked your warm and cold control pressures? Could be a fuel pressure issue.

Alternately, have you blasted around with carb cleaner and looked for vacuum leaks?

[john walker's workshop]

too much carpet and mat around the gas pedal. =)

[RoninLB]

Originally posted by john walker's workshop

too much carpet and mat around the gas pedal. =)

don't you all laugh.. it happened to me wearing clunky boots that pushed the mat foreward.

[echrisconnor]

Hey, that's why I wasn't getting WOT for a while. Fixed it and it was like free horsepower!

[Mysterytrain]

Update..I removed the vac line from the top of the decel valve. Plugged the line and plugged top of the valve. Went out and drove the car and got it good and hot. The rev's go down faster then Monica Lewinsky. Feels like carbs. The fast idle problem is gone. Problem is that coming off the throttle from high revs the car will die. I'm thinking defective decel valve.

[john walker's workshop]

they are adjustable ya know.

[Mysterytrain]

John, I've cranked the little bugger all the way down to the point were the rev's drop off fast (as if its plugged) but the idle crawls back up to 2K when the engine is hot. I think it leaks. I think there is another test I can perform ( from the shop manual) pinch off the rear hose that comes from the side of the unit, a change in idle indicates leaky valve.

[RoninLB]

Originally posted by Mysterytrain

go down faster then Monica Lewinsky.

Problem is that coming off the throttle from high revs the car will die.

I'm thinking defective decel valve.

In my CIS days I ran 1k rpm idle and a richer mix than spec O2.

"defective decel valve".. probably.

[Mysterytrain]

Figured I should update this thread..replaced the decel valve and that problem is solved.

[RoninLB]

Originally posted by Mysterytrain

Figured I should update this thread..

thanks