idle

[icarus-54]

Hi guys,recently bought zr-1 #361,and have a problem with the idle taking too long to come down.It takes sometimes over a minute to return to 750.It seems to come down in stages which makes me think its the iac.These cars are a totally different animal to me as I come from the sy/ty world.I don't believe its a vacuum leak as it does come back but its a real pita to drive. If anyone has any ideas,I would be most grateful.
thanks,Jack

It is the IAC and its doing what its supposed to do, at least based on the stock calibration for the 90. It can be changed and the rpm decline sped up. However, the LT-5 wants to stall and if the Throttle Follower reacts to quickly, it will do that. Modded motors are more susceptible to this. But before doing any cal changes, make certain everything is nominal mechanically. IAC and port should be clean. Make sure throttle plates are also clean. Check TPSv at idle. Should be > .53v but < .57v.
BTW, its an SD motor so many of the Sy/Ty stuff applies. I learned using an 84 Xfire. Much applicable when it comes to tuning.

[Kevin]

can you drop it by tapping the gas? If so I have the same problem and I emailed Mr. Haibeck, his response was


You might have two problems. If the idle speed can be reduced by kicking the throttle, the secondary throttle plates are probably sticking. The throttle body can be repaired.
http://www.zr1specialist.com/HAT%20Web/services/throttle%20body.htm

[icarus-54]

can you drop it by tapping the gas? If so I have the same problem and I emailed Mr. Haibeck, his response was

No,kicking the pedal or pulling back on the cable cam of the tb makes no difference.It will return to 750 but it takes forever which is a night mare in traffic.It seems to step its way down which is why I thought it might be the iac.

[csx4350]

I just bought a pristine 1990 with 22k, it has only been driven 300 miles since 2000 and it was doing the same thing. The idle was between 1,000 and 1,500 RPM and wouldn't come down. I put 2 bottles of Techron in it and filled it full of Chevron premium. I then drove it (spiritedly) to a business meeting, about 80 miles total. It runs great and the idle is now silky smooth at ~800 RPM.

Letting any engine sit isn't great for it. I don't believe the fuel & additive should have effected the idle of a TPI engine, but it didn't hurt. I think the driving was more what it needed.

[Schrade]

You need Marc's chip (should be end of discussion)...

[csx4350]

I've thought about that, but who is Marc and how do I get in contact with him about an Eprom?

[Dynomite]

I've thought about that, but who is Marc and how do I get in contact with him about an Eprom?

Haibeck Automotive Technology (http://www.zr1specialist.com)

Marc Haibeck is one of the best and super in helping us with technical issues :thumbsup: