I bought a p28 ecu off of a 94 civic ex with a skunk2 DOHC Vtec chip. For about 15k miles I have been running my 99 Si (b16a2) stock, with the execption of bolt on mods (CAI, TB, 4-1, CB Ex). My car has always idled at 700-800 rpms and run perfectly until I converted the ECU to OBD1 with this chip. I started my Si right up after the install and it seemed to run fine @ <1,000 rpm idle. I left and came back a few hours later and started my car up to go test drive and was disappointed by the rhythmic rise and fall of the RPMS from 1,000 to 1,500. Not only that but it seemed my car barely stayed running right after i started it. It bogged and shuddered around 500 rpms and then shot up to being erratic again. I am almost 100 percent sure if I put my OBD2 Ecu back in the problem would be gone (however I would then get the CEL from the test pipe again). What needs to be done electronically to my car to fix this idle problem? My coolant level has been constant for months and there appear to be no leaks or physical problems. My buddy had the same thing happen on his 91 Si with JDM SOHC ZC engine. However that was because of a leaky head cover gasket so I am really stumped right now. Any ideas or help greatly appreciated!

 

I'll take one from the Kenji book of idle treatment.

Unplug your evap purge solenoid (it's the only plug on the fuel rail) and that should take care of most of the problems. The idle will still surge a bit a warmup, but not nearly as badly as it would with it plugged in.

 

So I just unplug the solenoid and leave it unplugged? I remember reading in another forum something about how there are two sensors that control the idle, and with an OBD1 ECU on a b16 I guess it can't handle it. So I pull the plug out of the end of my fuel rail then? Like if you are looking at the underhood pic of my car it would be the little cap on the far left of the rail facing the CAI? Or am I looking for something more like the sensor plugged into the CAI? Thanks.

 

"It’s on the fuel rail. It’s on top of the fuel rail, about in the
middle. It’s the only other thing on the fuel rail besides the
injectors that can be unplugged. It has one vacuum line connected to
it and that line then goes to the intake manifold. You can’t miss it."

That's quoted from another H-T user and I saved it when I went to do this on my car.

I taped the plug up w/ electrical tape to prevent crud from building up in it.

 

here you buddy this might help...

https://honda-tech.com/zerothread?id=340334

judd

 

now i just tried this, i was expeirencing a similar problem. after the unplug should you expect a check engine code?

 

it's a vacuum leak somewhere
I had the same problem when i put the y8 manifold on my y7

 

Ok I have located the evap purge on top of the fuel rail and I have a question. It looks like a sensor plugs in right on top of this vacuum hose you are talking about. Am I unplugging the sensor only or disconnecting the entire unit from the fuel rail? Thanks a lot for the info, I'm sure this must be the problem. I have been driving my car on stock ECU for months without a hitch and then all the sudden I change to OBD1 and **** starts sucking. So if I still have this problem after I disconnect this evap purge then I probably did something really special to my car huh? (bad kind of special)

BTW - assuming this ecu isn't fried I have a stock b16a2 P2T OBD2 ecu in MINT condition I would like to sell. If it's worth 150 shipped to anyone just let me know otherwise I'll hang on to it. Thanks!




[Modified by CPAV, 4:49 PM 4/6/2003]