I have heard this problem is common to prelude's with the 2.0 so i'm hoping someone on this site could help me with this. I have a 90 prelude 2.0 Si with a five-speed. My idle goes up and down between 1500 and 2500 rpm. It used to only do this when the motor was cold and then it would idle normal after it got to operating temperature. Now it does it all the time even after its fully warmed up and driven. The ecu is showing codes 7 and 17, although a few weeks ago it was also showing codes 1(O2 sensor), 43(?), and 6(coolant system sensor). I don't know what codes 7, 17, and 43 are. I've heard replacing my TPS sensor along with my O2 sensor and cleaning the EGR valve would fix this but I don't just wanna throw parts at it and hope it fixes it. Also, my speedo works intermittently. Don't know if it's the speedo gear in the tranny or if it's a problem behind the gauge. My friend had an 88 prelude that had both of these problems but sold it without fixing them. If anyone has had this problem before and fixed it, I'd really appreciate any input on this. Thanx

 

Yes, all three of those things should fix your problem. Also, your speedo problem is probably with your VSS (vehicle speed sensor). I'd buy a new one when you order the O2 and TPS sensors

 

Code 7 is throttle position sensor. Code 17 is VSS. Does this generation have an Idle Air Control valve and a Fast Idle Valve?

 

i guess that's why my speedometer works intermittently. on the way home from work i noticed i also have a code 14. arghhh. i hate technology. i know i have an IAC but i don't know about a Fast Idle Valve. it's a b20a motor.

 

to stop the idle surge, go buy a new throttle body gasket....take the throttle body off, if it has a fast idle valve underneath, clean it out well, and clean all of the tb ports....

while it is out check the throttle position sensor (your code 7)....get out the voltmeter and adjust if it doesnt read close to .5 at 0% throttle...

get a new o2 sensor off this site, find a used one, you wont spend much, that should fix code 1....code 1 is when the heater fails...so you need a new one...

your vss is crapping out, thats the code 17...

the 43 is the o2 sensor reading out of range.....replacing it plus the throttle cleaning ought to clean that problem up....

i dont know if 2.0l motors have two coolant sensors or just one, either way, one of them is bad, i bet theyre not too expensive.....thats the code 6

i hope it all works out for ya....

 

thanks for all the help guys. i'll try all of the suggestions you guys have and see what happens. won't be able to get to it till the weekend though, worked 72 hrs last week and 56 hrs this week. i'll let you all know how it turns out though. peace out.

 

Before taking anything apart, unplug your IAC and make sure your base idle is between 500 and 600 RPM. If not, adjust this first and see if this clears up your surge. Next, remove the top cover of the fast idle valve. There is a thimble in the center with a donut shaped ring around the outside that is the seat for the thimble. This ring sometimes gets loose and can be screwed back down.

 

okay, i did some tests today before work and made some progress. i let my car warm up to temp and took my intake off and covered up the top hole(IAC) in the TB and the car's idle dropped to 750. I then covered only the bottom hole(FITV) which did have suction at full temp and my idle dropped a little but still bounced up and down slightly. i then covered both holes and my car stalled. that means i have to replace IAC and FITV correct?

 

Not neccessarily. Go about it the way I suggested and also make sure your coolant level is full and free of air. These valves count on coolant flow to operate properly.