Rough Idle and Hesitation.....Speedo Works Then Doesnt - Honda Prelude Forum : Honda Prelude Forums
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Old 07-18-2019, 11:51 AM   #1
Join Date: Jul 2019
Posts: 2
Singerjohn is on a distinguished road
I have an 89 SI 4WS B20A. It had been sitting for 2 years with a new engine replacements and transmission replacement from Japan. It had been running great until recently after I finally fired it up to drive. I noticed the speedometer will work and then stop working and my S3 light will Flash and then a check engine light will come on. Then all of a sudden the speedometer will start working again as normal. The odometer never stops working. The other issue is at times after it seems to warm up it will idle rough and then if I press on the accelerator to get the RPMs up it will smooth out this doesn't happen all of the time. Sometimes it's really bad at a take off but other times it's perfectly smooth. I notice it will also run rough when the fan comes on at times but seems to run smooth when it's cool for a few minutes. The running rough just started. A week or so ago. At first it acted like a slight misfire. Now its worse. All new plugs, cap, rotor, wires when rebuild was done. I recently put a new cat converter on it and its OE spec. It was only driven about 2000 miles before I parked it. The speedo cable is new also. It always worked fine before I parked it also. Any ideas?

Last edited by Singerjohn; 07-18-2019 at 11:57 AM.
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Old 07-24-2019, 10:47 PM   #2
Getting Comfortable
Join Date: Dec 2012
Location: Wyoming, USA
Posts: 34
richrd0001 is on a distinguished road
Speedo and performance problems

I had odometer issues with my '89 SI. I replaced the speed sensor in the back of the instrument panel and solved the odometer problem. The old sensor had stripped gears as I recall. I can't recall if the speedometer was also a problem. I seem to think I did. Anyway, the new sensor brought it back to life if there problems before but now I have occasional periods where the speedo drops to zero when I'm driving but then after a short while comes back. Mostly it's ok. I checked all the circuits on the back of the instrument cluster so no breaks, though I suppose there could be a relevant circuit with a break affected by heat.

I just solved a crank/no start problem by merely bleeding the cooling system. My machine had sat for about six months during the winter and suddenly wouldn't start. I wasn't getting any codes and someone mentioned bleeding the system in one of the FAQs. I tried it and shazam!

Theoretically I don't know why an engine coolant temp bathed in cold coolant versus not being in coolant (but still cold) would send different info to the ECU. The sensor has high resistance when cold in either case.

Be that as it may, it's easy to bleed the coolant and give it a shot. My impression is that the coolant temp sensor has a big effect on starting and running.

You are getting no codes?
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