High idle and no codes

RS01

New Member
This one is testing us. Swapped out the high mileage B18A1 motor with a newer one and bolted most of the items off of the 90 motor to the 91. Not a bad swap and the 91 motor is way better than the 90 (not so tired and noisy). The problem is the idle and we can't get it below 1250. On the old motor it took about a 1000 miles before it settled down (needed a lot of work and still didn't get all the codes addressed). We now have no codes and I'm wondering if the ECU is tired. O2 replaced, TAS replaced, vacuum checked, injectors replaced, etc. Seems to be running a bit on the rich side since fuel consumption is up from before the motor swap.

Stumped.
 

hgocasca

level 77 troll
Iacv or the other intake sensor right by it, the name is slipping my mind. Remove and clean them both then replace. Should be your problem.
 

RS01

New Member
We have checked them per the manual and they checked out ok.But we have not cleaned them and that is something we can do.
 

Amiguel6

New Member
Yes. Flush them out thoroughly. Also, adjust the screw in the Fast Idle Thermo Valve if needed
 


RS01

New Member
I haven't put a scope on it yet because the idle was so high. I did move the distributor back to get the idle down from 1500 to 1250. This weekend we are set to work on it.
 

d@_b3st

New Member
have you checked for vacuum leaks? spray carb cleaner or starting fluid around IM gasket and or TB gasket, also are the o-rings on the injectors good?(not cracked or dry) i'm guessing it could be a vacuum leak since you didn't mention idle fluctuation which could be the iacv.

hope this helps, keep us posted
 


Nick_C78

New Member
First post says he checked for vacuum leaks.

Let me ask a stupid question though... Do you let it warm up, or is it just idling high when you first start it so you guys turn it off? Also, have you checked the throttle cable? If is VERY common for people to make it too tight, which causes the throttle not to close all the way. I can't tell you how often I see that.
 

RS01

New Member
You are correct in that we have been all over it checking for vacuum leaks (it would be a simple fix!). No leaks have been found and I have used a vacuum gauge/pump to test lines and valves.

The car is warmed up and it, in fact, is driven almost daily in spite of the high rpm. Before we did the motor swap it did this and it eventually settled down.

Just found out the right rear bushing is bad so we will limit the driving until it is replaced but it is ran and fully warmed up.

Yes, the throttle cable has been checked but I will check it again.
 

BigMac88

Fat guy in a little 'teg
Check your fast idle control valve and throttle position sensor. Also make sure your TB gasket isn't leaking. My friend had the same issue on his 92 and it ended up needing a new fast idle control valve.
 

RS01

New Member
The good news is that I have a factory shop manual and was able to test the fast idle control valve when I first posted and it passed both the cold and warmed up test.

Which puts us back at the IACV. Was able to go out and do a quick clean while the motor was warm. RPM's dropped immediately to about 1K. A huge reduction and I think we are on the right path. Will do a more detailed cleaning when the motor cools.
 
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RS01

New Member
I was able to clean the IACV a little better and the idle dropped to 750. That was when we put a scope on it and timed it. It has since returned to a higher idle of about 1100 after it had a cool down and restart, which leads me to think that it's time to replace the IACV.

Waiting to see how the alignment comes out tomorrow. Wanting to turn this car loose on the road and log some highway miles before we do much more.
 
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