Idle Problem 90 MTX

[shomandan44]

OK, let me try this again in the Generation I forum. I have been experiencing an idle problem on a second start (warm start) after starting the car and letting it warm up for about 5 min’s. The engine was re-built about a year ago and not driven since. It was re-built with 207K on the car and since then it has had the same problem. There is a “surge idle” after the second start that can be initiated by turning on the parking or head lights but not every time. It is totally inconsistent! The battery is good, cables are new and almost all of the add on parts have been replaced. The problem is very erratic and usually on the third start it runs fine again. The ERG system was removed as this was a California Car originally. The EEC was replaced but made no difference and since then the original has been re installed. The OBD codes do not indicated any problems and the CE light is not on at all, but did come on for a while. Any thoughts would be appreciated. Thanks to all

 

[luigisho]

THere was a common issue with the light and dimmer shorting. I wonder if it is electrical draw from that or the battery/charging system. Why did you reinstall the original eec if you deleted the egr? I can't believe that doesn't trigger a code

 

[shomandan44]

THere was a common issue with the light and dimmer shorting. I wonder if it is electrical draw from that or the battery/charging system. Why did you reinstall the original eec if you deleted the egr? I can't believe that doesn't trigger a code

Interesting that I just went out and started the car and when I attempted to adjust the dimmer for the dash lights the idle problem started again. I will remove the dimmer switch and check it out. Thanks for the info. Do you know what the common problem was with the dimmer?
The old EEC IV does not throw the Check Engine Light but does indicated the EGR valve is not opening so you are correct is does recognize the missing EGR valve.

 

[luigisho]

I think it was shorting out and I remember one or two maybe catching fire? Most failures did not do that and it's been so long since I had issues with one I forget why I had to replace it. But I would check that first. If you need a used one try Dan Barbush SV&HOdan on the board. He parts old SHOs and his prices are always reasonable vs other places

 

[zoomlater]

I think it was shorting out and I remember one or two maybe catching fire? Most failures did not do that and it's been so long since I had issues with one I forget why I had to replace it. But I would check that first. If you need a used one try Dan Barbush SV&HOdan on the board. He parts old SHOs and his prices are always reasonable vs other places

was that the headlight switch that would melt

 

[luigisho]

was that the headlight switch that would melt

Yeah. Saw a few of those posted over the years. Most just shorted and started doing weird electrical things that made you replace it.

 

[BaySHO Performance]

The '89 multifunction switch occasionally overheated and fried the connectors. It was redesigned for the
'90 which got rid of the problem, but that switch can't be retrofitted into an '89. Solution is to install relays in the headlamp circuits to get power directly from the battery.

But I've never seen a problem with the dimmer switch or autolamp module shorting out.

 

[shomandan44]

The '89 multifunction switch occasionally overheated and fried the connectors. It was redesigned for the
'90 which got rid of the problem, but that switch can't be retrofitted into an '89. Solution is to install relays in the headlamp circuits to get power directly from the battery.

But I've never seen a problem with the dimmer switch or autolamp module shorting out.

The dimmer in my 1990 was bad about 20 years ago and I repaired it. The reostate design was terrible. When I checked it on Friday I realized the fix that was made had failed and could have been a potential problem. In researching a replacement I noticed that they had been re-designed and hopefully will be helpful. I also removed the fuse #8 which powers the dimmer circuit but unfortunately the idle problem has still not been resolved. I will replace the dimmer and continue looking for the issue.

 

[FastCAD]

OK, let me try this again in the Generation I forum. I have been experiencing an idle problem on a second start (warm start) after starting the car and letting it warm up for about 5 min’s. The engine was re-built about a year ago and not driven since. It was re-built with 207K on the car and since then it has had the same problem. There is a “surge idle” after the second start that can be initiated by turning on the parking or head lights but not every time. It is totally inconsistent! The battery is good, cables are new and almost all of the add on parts have been replaced. The problem is very erratic and usually on the third start it runs fine again. The ERG system was removed as this was a California Car originally. The EEC was replaced but made no difference and since then the original has been re installed. The OBD codes do not indicated any problems and the CE light is not on at all, but did come on for a while. Any thoughts would be appreciated. Thanks to

The dimmer in my 1990 was bad about 20 years ago and I repaired it. The reostate design was terrible. When I checked it on Friday I realized the fix that was made had failed and could have been a potential problem. In researching a replacement I noticed that they had been re-designed and hopefully will be helpful. I also removed the fuse #8 which powers the dimmer circuit but unfortunately the idle problem has still not been resolved. I will replace the dimmer and continue looking for the issue.

Did the rebuild include a new IAB (idle air bypass)? This can cause uneven idle and "surges" like you describe. The IAB does NOT throw a code. Get the engine warm A/C off and then dis-connect the IAB. If there is no change then "clean or replace". The Yamahammer should idle @ 800 rpm with the IAB dis-connected and 1000 rpm connected.

 

[shomandan44]

Yes it has been replaced. I replaced it with a new one from SHO Source and it appears to be working. I am in the process of replacing the EEC IV as I believe this is a problem and hope it solves all of the problems. I will look at the IAC (IAB) when running and see what the idle actually is. I have looked at the idle air twice and I do believe it is OK. Thanks.