phathick

Hey everyone, i have a 91 SI hatch, it has a Obd 0 B16 in it. Mods that are done are OBD0 to OBD1 Rywire conversion, Supertech Springs and retainers, Buddy Club Spec III Cams and gears ( Intake is advanced 2 Degrees) RC 370 injectors, Blox Intae Manifold thats been ported with a Blox 76mm Blox Throttle Body, and MSD 6AL. The car has a Walbro 255 pump in it. the car is tuned on Chrome and runs great but sitting still it Idle surges. I have replaced the IAC several times along with even holding finger over the hole in the throttle body and it still does it. With the hole covered its rough as hell and with it open is smooth but up and down it goes. With the hole open I can hear the IAC click open and close with the surge and after a ew sureges it idles so low it cuts off. What in the hell could it be that ould make this thing do it with or without the IAC. I have checked the Valve Clearences, Fuel Pressure, and for Vacume leaks and nothing adds up. Now I have even taken another ECU with Chrome on it out of a friends car that runs perfect in his car and put it in mine and it still surges and I have put mine in his car and it runs fine. SO ITS MY SET UP. No check engine light either!

Fabrik8

Sounds like it just needs more tuning at idle. Do you have a lightened flywheel, and has it been added since that engine was originally tuned?

phathick

yeah it has the ACT prolight solid Flywheel in it. and it has been in there since day one. As for the tune ithas been looked at over and over again. As for driving its great, its just sitting still. Like I said i can put my ECU in my buddys car and it idles fine.

Fabrik8

Lightened flywheels sometime cause problems like that; the inertia of the engine is less and the ECU will overshoot during idle regulation. The ECU expects the engine to take a certain amount of time to change rotational speed at idle, etc., and all of the factory calibrated time constants are set around that. Lower the intertia and the engine responds faster, so the ECU is making idle changes on a different calendar than the engine. This can usually be tuned around though. That Pro-Lite flywheel is really light, so it may be compounding that problem. You may also have a sensor that is on its way out. Think about the differences in setup between your car and your buddy's car, that may give you some idea of what you're working with and what is going on.

I still say it probably needs more tuning though, unless there is a sensor problem somewhere. When is the last time you checked your throttle position sensor and MAP sensor for correct readings? Oh, check the coolant temp sensor also, and the fast idle thermo valve (FITV) according to the factory manual.

92dx757

id be willing to bet the blox tb doesnt have a fitv which would cause a bit of an idle problem...put the oem tb back on

phathick

The Throttle body doesnt have the Valve on it. i have been reading and i was thinking about checking the TPS and coolant Sensor. the map is ok. Tried two other ones and the readings are fine. As for the differences in mine and the other car, its the same clutch and flywheel. His throttle body doesnt have the valve either so when I get a chance im going to check the TPS first.