Mechanics

90 PRELUDE SI SURGING PROBLEM

1990 All Other Makes All Other Models

I'm having a surging problem with my 90 Prelude SI. It has the 2.1 motor, 5-speed. This motor/trans is from a 91 Prelude that I installed in the 90. The motor has 123,000 miles on it. Starts up with a high idle and stays at about 2,000 rpm. After about two minutes the motor starts to surge from a high idle to a low idle and just keeps doing it. The service engine light does not come on so I don't have any codes to look for. I'm scratching my noggin' on this one. Any help what to look for would be appreciated. Thanks in advance.
Avatar
Ludedude
November 18, 2006.




I could be a faulty idle air control valve or one that needs to be cleaned. It could as well be that the cooling system needs to be purged of air. Did you by chance do anything to the intake manifold at all? A vacuum leak will cause the surging.

Bruce Hunt
Nov 19, 2006.
Thanks for the quick response to my question. I bled the cooling system once the car was running again. I did change the intake gasket when I installed the new cylinder head. Also cleaned the intake up well. I do have a spare idle air control valve from the old intake and will try that to see if that takes care of the problem. I'll let you know what happens once I change the iacv.

Tiny
Ludedude
Nov 20, 2006.
Hello Bruce, I changed the eacv on my lude today and it didn't solve the problem. May be due to not having enough coolent in the system at the time. I then changed the fast idle valve and air boost valve. I cleaned all the valves before replacing them. That brought my idle down, once warmed up a little, and the surging started again at a lower rpm. I gave the motor time to get hot so the thermostat would open and than topped the cooling system off with anti freeze. The surging stopped and now I have my normal idle and it's smooth. Not sure which piece solved the problem but so far so good. I'll know better tomorrow when I run it. I just hope the doors don't fall off next. I also changed the power rack about two months ago and the motor surged until I topped off the power steering fluid. Guess the ecu on these cars are finiky.
Again, thanks for all your help.
AD

Tiny
Ludedude
Nov 24, 2006.
Hello Bruce, I have to update this post in the event another Honda owner has the same problem that I had. My lude started to surge again so I double checked the cooling system to make sure I didn't have any air trapped. It seems I didn't purge the cooling system well enough the first time I did it. There was a lot of trapped air in the system. Once it was purged everything worked perfect. The idle dropped down and there is no more surging.
Thanks again for your help.

Tiny
Ludedude
Nov 29, 2006.

AD