I have a 92 Civic VX with the stock D15z1 engine. The guy I bought it from put a cold air intake on it and switched the ECM from the stock P07 to a P28. The car runs fine but is very slow until it hits 4800 when the VTEC hits. The engine light is always on and the gas mileage is less than it should be. I changed spark plugs recently and found that they are burning a little rich but not too bad. Recently I bought the stock P07 ECM for it so I could get the gas mileage that the VX should get. I am getting 35-40 with P28, P07 should get 46-52 (so I hear). When I hooked the P07 up my engine light did not come on anymore and it idled very smoothly and evenly. When I took it on the road I was pleasantly surprised at the amount of low end performance I had gained. After burning up and down the strip about 10 times it was time to head home and thats when I noticed a strange problem. I cannot hold a steady speed without the engine bogging down like the cat. is plugged. As soon as I lift my foot a little it comes out of the bog and if I apply more accel. it comes out of the bog. It doesn't sputter or jerk or chug, it just bogs down like its got the choke open or something. My question is, would running the rich burning P28 ECM for a year clog up something or mess something up so that it runs ok but a more conservative ECM runs poorly. Its very strange. The car runs very strong under full accel and idles fine. What could cause a no-load bog like that. I am running the P28 again with no problems except for poor low end and my engine light stays on. If anyone has some real understanding of the VX VTEC-E engine and what may be the prob, PLEASE respond. If anyone figgers it out Ill send you the amount of money I save on gas for a month, and I drive alot....Thanks gang

Purple

 

im just guessing off of the top of my head, but my first instincts are the cat and O2 sensors got fouled up from running rich.

 

You need to see what check engine light you are throwing before anyone can really help you.