My newly mild streetported engine is running fine and smooth when driving, but at idle it coughs/stutters.
Running everything stock including ECU.
What can cause this? Bad timing? Running too rich? Is it bad for the engine to run like this?

Film clip, engine at idle

 

Bump.

 

Your video link doesn't work.

What rpm is it idling at? Is the idle hunting (reving up and down)? We need more info please.

R.K.

 

Odd, the link works fine here. http://macen.nullnet.com/film/DSCN1308.avi

It's idling at 800rpm and is not hunting.

 

The link worked fine here (SAVE AS).

Unless the *mild* streetport is not so mild then it does seem to be running a little strange at idle. I would start by checking the following:

1. O2 Sensor. If you didn't replace this with the engine, now would be a good time.
2. TPS adjustment. Make sure the TPS is adjusted properly
3. Spark plugs. If seen some new rebuilds foul plugs pretty quickly in the beginning. They can usually be cleaned with a spark plug cleaner if you have access to one otherwise just change them out after about 300-400 miles.

 

Sorry, I should have added this earlier in the thread:
TPS is checked via my Power FC (connected it just to check the voltages, now I run stock ECU). Voltages at idle and at WOT are within specs.
I have tried with new plugs (BUR9EQP L & T) but no change.

Haven't replaced the O2 though.

I have also removed the IM and checked all vacuum hoses, and they are connected correctly.
Plug wires (NGK) are brand new.

Thanks for your replies.

 

Here's a good thread for you to take a look at:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/driveability-improvement-secondary-throttle-plate-adj-o2-sensor-repl-687859/

 

Thanks. I will give that a try.

 

Macen,

I had that exact issue as you. I also had a mild streetport with the stock ECU. I tried several grounding points, checking plugs, new O2 sensor. And nothing. My understanding is that with the stock ECU the O2 sensor readings are all jacked due to the porting. So the control system keeps on trying to correct it self and what you end up is with a cough at idle. Or a miss.

FYI- My fix came when I got a Power FC.

 

montego: Good to hear, I had that in my mind too that the stock ECU is the problem. I will have the engine maped with the Power FC then. But first I need a bigger IC and probably a V-mount. Already got a Koyo N-flow rad. :-)