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Hello guys, I have a 1994 Prelude 2.3L with an automatic transmission. I’m having a weird idle surge with it and it’s driving me crazy. As the engine warms up the idle is within normal range, idling at 650-750 RPM’s, but if I give it a little gas or if I just tap the gas pedal slightly the idle will surge to about 2k and then you can hear a “pop” coming from the intake and the idle will return to normal. Doing this while driving in reverse or drive the idle will jump up to about 1400 RPM’s and idle there, If I let go of the gas while the idle is at 1400 the rpm’s will climb and then I would hear that pop from the intake and the idle will return to normal, but giving it gas the idle will return to 1400. This all started about a year and a half ago when I took the car in for service, the mechanic noticed my car would die when at operating temperature, instead of figuring out what the problem actually was he tried to mask the problem by keeping the throttle open, messing with the idle screw and stuff. He even told me to get him a new throttle body and IACV and after I got the car back it started to do these symptoms. Fast forward to now and I replaced all the intake manifold gaskets, and even tried a different IACV and ECU. I got a vacuum diagram for my car and followed all the hoses to make sure none of them were misplaced. I even took them out one by one and plugging the port with no luck. Things I noticed since these symptoms appeared is the intake sucking these cars make when you have an cold air intake isn’t as loud as before, actually it’s very faint now and you can only hear it if your ear is right by the filter. When I take out the vacuum hose from the intake to the MAP sensor the surging will stop, but I tried another MAP sensor with no luck. I have no CEL and everything seems in the right place, Any ideas on where to start? Thanks
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It’s backfiring through the intake because the timing is off probably. When you open the throttle it advances timing and when it snaps shut the computer will retard timing a lot and that would be intake backfire because the timing is off. Retime distributor base timing. Under dash passenger side. 2 wire connector. Jump the 2 pins and set base timing to I believe 13-15 degrees. That’s what I usually set them at with no issues. Check under hood decal just in case. It’ll have base timing. Report back after retiming. If it doesn’t change symptoms or cure the problem. Floor the accelerator and see if it has any power or just stumbles. If it does you either need a timing belt or if you just got a timing belt it is timed wrong and you need to redo the timing belt.
The mechanical and ignition timing of the engine have been checked and they are not off. I didn’t mention that I recently swapped this engine with a used engine from japan. My old engine had the same problem. I swapped the intake manifold from my old engine and everything was marked before the swap and rechecked again using a vacuum diagram. I tried to fix this issue when I had my old engine with no luck.
Tried 2 different ECU’s and nothing. Someone told me it could be a problem with the EVAP system, but I don’t know where to even start.
Bypass the evap hose and see if it makes a difference. I don’t think it would but it’s a possibility.
https://www.youtube.com/watch?v=KuXCT23oXqg Here’s a video of it. Maybe you can tell a little bit better this way.
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