Idling problems with a JDM 12AT engine

Rotary Engine Chat......Got A Problem With Your Rotary Engine.... Need Help...?
User avatar
Traxnada
Posts: 89
Joined: Wed Sep 23, 2015 3:57 am

Idling problems with a JDM 12AT engine

Post by Traxnada » Tue Nov 01, 2016 8:17 am

Hello guys!
So, I recently replaced the trailing ignition control unit on my JDM '85 12a Turbo (EFI). Now the car works like it used to and I'm VERY happy with the results!
I still have a little problem with idling though. I would have thought changing the ICU would fix the problem, but nope...
Description: When cold, the idling makes me think a bit of a cammed V8 engine. It has some kind of a weird rhythm to it that has nothing to do with a rotary. Once the engine gets a bit warm, idling stabilizes itself but way too high, around 1300rpm. If I give it a bit of throttle (up to 3500-4000rpm) then let the RPM fall down to idling, it will stabilizes around 700rpm (a bit too low), but just merely touching the throttle, sends it back to 1300/1400rpm right away.
If I shut down the car for a couple of minutes, then turn it back on, the idling will be CammedV8-ish for 30s, then stabilize again at 1300-1400rpm.

Other than that, everything is great with the car. No problem at all, great throttle response and tons of fun. It's just this idling problem that is a bit annoying since my car is daily driven.

If anyone has an idea as to what might be wrong, I'm all ears :)

Thanks,

Flavien

User avatar
Hobbawobba
Posts: 1255
Joined: Tue Nov 01, 2011 9:44 pm
Location: Worcester - UK

Re: Idling problems with a JDM 12AT engine

Post by Hobbawobba » Tue Nov 01, 2016 12:01 pm

I don't have a clue what the problem would be. But maybe uploading a video on Youtube might help a bit? :)

User avatar
Traxnada
Posts: 89
Joined: Wed Sep 23, 2015 3:57 am

Re: Idling problems with a JDM 12AT engine

Post by Traxnada » Tue Nov 01, 2016 2:01 pm

Hobbawobba wrote:I don't have a clue what the problem would be. But maybe uploading a video on Youtube might help a bit? :)
OK I'll do that tomorrow then :)
11pm here already so...

KiwiDave
Posts: 1762
Joined: Sat Nov 05, 2011 8:07 pm
Location: Feltham, Southwest London

Re: Idling problems with a JDM 12AT engine

Post by KiwiDave » Tue Nov 01, 2016 5:31 pm

Sticking throttle cable or throttle body?
1985 Sunrise Red S3 TWR
2003 Mercedes E320 CDI Estate AMG

User avatar
myatt1972
Posts: 1437
Joined: Thu Mar 31, 2011 10:54 am
Location: Staffordshire Moorlands

Re: Idling problems with a JDM 12AT engine

Post by myatt1972 » Tue Nov 01, 2016 9:10 pm

KiwiDave wrote:Sticking throttle cable or throttle body?
My first thought to Dave.
Keith...

KiwiDave
Posts: 1762
Joined: Sat Nov 05, 2011 8:07 pm
Location: Feltham, Southwest London

Re: Idling problems with a JDM 12AT engine

Post by KiwiDave » Tue Nov 01, 2016 9:27 pm

myatt1972 wrote:
KiwiDave wrote:Sticking throttle cable or throttle body?
My first thought to Dave.
rdg th:
1985 Sunrise Red S3 TWR
2003 Mercedes E320 CDI Estate AMG

User avatar
Traxnada
Posts: 89
Joined: Wed Sep 23, 2015 3:57 am

Re: Idling problems with a JDM 12AT engine

Post by Traxnada » Wed Nov 02, 2016 2:32 am

So I just came back from the car... Of course, because I was trying to shoot a video it hasn't caused as much problem as usual :lol:
Nonetheless, you can hear what I mean by weird CammedV8-ish idling at 4min40 and 6min05 in the video.
I will look for a slightly stucked throttle cable, but I doubt it is the problem... Could be nonetheless so I'll WD40 the shit out of the cable, we'll see :)


User avatar
Hobbawobba
Posts: 1255
Joined: Tue Nov 01, 2011 9:44 pm
Location: Worcester - UK

Re: Idling problems with a JDM 12AT engine

Post by Hobbawobba » Wed Nov 02, 2016 11:05 am

Oh that does seem quite strange (to me at least). Wouldn't a stuck cable would keep it at the same RPM rather than fluctuating? Love the car by the way! :o

User avatar
Traxnada
Posts: 89
Joined: Wed Sep 23, 2015 3:57 am

Re: Idling problems with a JDM 12AT engine

Post by Traxnada » Wed Nov 02, 2016 11:19 am

Hobbawobba wrote:Oh that does seem quite strange (to me at least). Wouldn't a stuck cable would keep it at the same RPM rather than fluctuating? Love the car by the way! :o
Yeah, I doubt that's the problem either... To make it jump back from 700 to 1300rpm, I also merely have to touch the pedal, not even really pressing it. Not pressing it enough to make to gain 600rpm anyway...
And thanks :)

DB RX63
Posts: 695
Joined: Mon Apr 02, 2012 10:52 pm
Location: South East UK

Re: Idling problems with a JDM 12AT engine

Post by DB RX63 » Wed Nov 02, 2016 5:35 pm

Check all of the ignition components, plug leads, coils, distributor cap and rotor etc. Often these things can be electrical when they seem mechanical.
Met Blue Series 2 Elford Turbo
S3 Rally Car (under Construction - Nearly Finished !)

Post Reply