erratic idle?

[welsh_monty]

Afternoon one and all

I have not long ago started on my Zed adventure, but I would like a bit of advice,

 

I can start my car like a dream, fires up and idles fine....but sometimes if you were to rev it the rpm would drop to almost stalling, but other times she is fine.

I'm new to these engines so before I go looking for a problem that isn't there, has anyone else had this happen to them?

any advice would be greatly appreciated

thanks

Monty

[Gaz 300]

Can be hard to find a fault for this sometimes but when I had this fault with my old Z it was the connections of the coolant temperature switch that just needed cleaned. Here is a good link to problem solving http://zhome.com/ZCMnL/PICS/hesitation/hesitation.html

 

[dougal200]

Welcome along to the exciting and often frustrating adventure.

 

If I were to guess then I would say that the idle control valve is probably set too far closed. The manual screw is often confused as the idle speed adjustment where as it actually adjusts the balance between how much air the idle valve lets in mechanically/via the solenoid.

 

Basically when at idle, you want the solenoid operating as slow as possible (it pulses open and closed many times per second).

 

Tightening the screw in blocks off the bypass so less air goes in and the solenoid has to open more to meet the target rpm. This is fine in steady state idle but when you Rev it and let the revs drop the ecu tries to stop the engine stalling, however if the valve is already operating at 85% for example it has very little reserve to allow more air in to stop the stall.

 

Sorry for the very wordy answer.

 

Actually to get this all right you really need a data scan etc, they are very cheap off eBay and are really invaluable for these cars.

 

There are quite a few guides out there for really setting these cars up right, once done you will be amazed how smooth they are.

 

You should also chech the following

 

Boost leaks

Timing

Corrosion on all connectors

Throttle position voltage

All fault codes

 

Actually once you familiarise yourself with the engine, they are not that bad

[dougal200]

Here is a much better explanation

 

https://z32.wikispaces.com/Idle+Control

 

And a great service/tune up guide

 

http://www.twinturbo.net/nissan/300zx/forums/technical/view/922678/The-6-Ps-Proper-Preparation-Prevents-Piss-Poor-Performancegt.html

[welsh_monty]

thanks for the links there and all the advice, once I get to the source of the problem I will let you know what it was in the end.

thanks again for the advice! :w00t: