Rep Power: 777

I just put a D15b in my 93 DX Hatch. I also installed the p28 computer to go along with it. Now when i start it up it starts all fine, but at idle, it revs up and down continuously....its fine when i give it gas...but when it goes back down to idle it does this again. Anyone know why it may be doing this and what the solution is? Thanks!

 
Rep Power: 803

does it do it al the time or just at start up when its cold..
mine does the same thing but about 5 minute after it warms up, it stops

 
Rep Power: 777

Well I'm not sure yet, its still in the shop and we havent had it running for long enough to know that...but it is in a heated shop so its not really cold.

 
Rep Power: 803

yeah.. but the motor is still runing cold.. believe me, a heated shop will not hit block temperatures..
i bet if you let it warm up, it may take the reving away.. the first time i started mine up, i was like WTF.. but when i drove it, by the second set of lights it was running smooth....
give it a shot, if it doesn't work.. then it could be vacuum lines, maf sensor with vac lines going to throddle body.. who knows..

 
Rep Power: 777

If the problem persists even when the car is warm, I can almost bet that it is the fast idle valve. It's located under the the throttle body. If the problem goes away when the car is warm, I would say it's the Idle Air control valve which is located on the back of the intake manifold. Hope this helps.

 
Rep Power: 0

It is totally normal for honda rpm to jump while idle until the engine reachs operating temperatures

 
Rep Power: 787

Its like a barrel valve . If the motor has been sitting for a while it might be stuck , or jamming up . You can try soaking a little stuff like crown rust control lubricant in it . And use the BACKSIDE of a piece of emery paper too polish the barrel a bit . Not the front , rough side , that will scratch it . Turn the barrel and keep the paper against it . It might help , I do it sometimes at the shop where I work . We sometimes run across honduhs where the valve sticks from sitting for a while . Not the by the book perfect way to do it , but it might help..77.

 
Rep Power: 0

Revving up how high?

What is normal idle rpm for that engine?

Throttle possition sensor, idle speed control valve, vacuum leaks...Just to name a few possibilities.

 
Rep Power: 777

Alright took it out for a drive tonight and its still doin it, so that takes away the possibility of it being "cold". Now one thing I did notice is that my oil temp gauge isnt moving, its sitting at dead zero n doesnt move. Don't know if this is directly related at all tho. I'm going to be getting the codes run on it tomorrow hopefully so I guess I'll be going from there!

 
Rep Power: 787

If it kinda revs up , then drops quickly, almost to the point of stall out , stumbles , then catches itself , then repeats the cycle . Its probably the idle speed is stuck.So far in the last month , we,ve had 2 civics and a 3.0 cl do it .Still check for leaks and stuff , timing , etc..77.

 
Rep Power: 777

Definately not that...never comes close to stalling...always just a little rev then back down to what sounds normal for idle and its systematic like a heartbeat, always in synch. I dont have a tach as i havent installed my SI cluster but thats cuz i hit a roadblock there too

 
Rep Power: 0

There was a civic in woodbridge last year that idled from 1000rpm-2500rpm jumping up and down. It had a messed up throttle cable. It was to tight or kinked somewhere...something like that. May as well check that out as well.

 
Rep Power: 0

it's the idle air control valve located on the intake manifold, we got plenty in stock pm me if you need one.

-mayo

 
Rep Power: 777

UPDATE: I installed my Si Cluster today so now I have a tach, and at Idle it sits JUST below 1500, then when it revs up it revs up to meet 1500, then drops back down just below it and repeats the process.

 
Rep Power: 0

it's the idle air control valve located on the intake manifold