ZackZ420

Hello Fellow Third Geners. Sorry this may be repetitive. My 91 Z 305 is idling and shifting way to high. So on cold start it will be at 2500-3000 RPMs then when warm goes down to a whopping 2000-2250. With lil surges sometimes. Driving casually will shift at 4500-5000 til I can get up to speed and in OD then will go down to 3000 rpms. so at 60 MPH it will be almost at 4500 rpms. Should b way lower? So came on here and did some research. replaced some vac. lines. There is one going to firewall? Hard to replace? Climate or Cruise? Then sprayed Starting fluid around Throttle Body and Plenum and runners. No change in RPMs. Bought a new IAC. was looking at reset instructions but I can't get the rpms even in the ballpark let alone under 1000. But even when I unhook IAC no change in RPMs. I even backed off the throttle screw and still nada. Thanx Guys for any input and have a great day.

KyleF

Ouch, yes way lower unless you are driving 120mph.

This is interesting, are you saying that when dirving at 60mph you are seeing 4500RPM? In OD? Does your engine sound like it's turning that fast? That RPM should be near top speed!


Climate

Did you force it closed before unplugging it?


I am sure you have seen this on your research, but do you have anyway to read/log ECM data?

ZackZ420

No have no way of logging data. I have a cheapo tool to read blink codes. Yez correct on RPMs and if i get it to 70 ill b in the yellow. And does that mean force close the throttle?

RBob

iTrader: (1)

Sounds like your tach went out:

https://www.thirdgen.org/forums/elec...meter-fix.html

RBob.

ZackZ420

Is there anyway to hook a different tach up temporarily to see? I still think its revving way to high but could try to eliminate any possibility. I dont wanna burn out a valve or mess up the tranny.

KyleF

Force the IAC closed. In the reset (or minimum idle set) one of the steps is to ground the terminals on the ALDL with a paperclip so the IAC will close. Then you unplug it. If you unplug it while it is open, you are just dealing with an open passage on the TB.

One of two things are going on here IMO.

1.Your tach is either bad or the ICM is sending bad signals to it. Yes, you can go to a parts store, buy a cheap sunpro tach or other brand, and hook it in per the instructions

However, you say the engine actually sounds like it is turning these RPMs so...

2 Transmission is slipping something awful while driving. Though, that doesn't explain the high RPMs while parked which as Rbob says follows #1.

Can you upload a video to Youtube or another service and link it here. Just show it setting in your driveway idling and the tach.

thtanner

iTrader: (1)

HF does have a stand-alone tachometer...

https://www.harborfreight.com/lcd-au...kit-95670.html

Good to have in the tool box even though you should be able to hear this one by ear.

KyleF

You didn't really answer if your engine sounds like it is turning high RPMs. When setting in your driveway and adjusting the throttle stop screw there would be a big difference between turning 750 RPMs (about what warm idle should be) and 2500 RPMs. If it sounds like you are at 750 but tach reads significantly higher then the issue lies in the tach or signal to the tach.

vinny R

If your car surges with the increase in RPM, well your tach is not the only issue. I had this exact issue a couple yrs. back and when my RPM's went up the car physically surges, you can feel the engine increase not just watch the tach go up. It was my TPS sensor, the one on the TB. The strange thing is I am now on my second one. About a yr. ago I started noticing that the car would just start that idle jump again ordered a new one and problem solved for how long is the question>

ZackZ420

The First one is the idle and the second is driving. Yes to answering if it sounds different. Was going to try TPS next get the good old volt meter out and test.

thtanner

iTrader: (1)

Tach - if you were at 2500rpms it'd be screaming!!

Car sounds fine.

You can reset your TV cable for the transmission, there is no adjusting it per-se, its just set via the procedure.

RBob

iTrader: (1)

Engine RPM is OK, tach is bad. See link previously posted for the fix.

RBob.

KyleF

100%

That idle sounds spot on TBH. It is definitely not actually running those RPMs.

ZackZ420

Omg!!!! Thank you guys so much. I thought something was seriously outta wack!!!