I'm running a boosted d15z1, just got it on the road a month ago. Runs good, boosts to 5-6psi. It's in an obd0 chassis and I'm running it on the correct civic vx 49 state obd1 P07 ecu with the 5 wire O2. I've got code 48 but I think I know why.

My problem, though, is that while running around 3K, if I let off the gas just a little, or step on it just a little, the tach drops to 500 rpm or so. Step on it and it goes right back. Doesn't affect the performance at all. Car runs the same whether the tach is jumping or not. Doesn't die. My cruise shuts off at the same time so I assume the ecu is not sending the tach signal out when this occurs. No codes other than 48. Any ideas? I was thinking bad tps?

 

bad cluster maybe

 

Check whether the blue wire attached to the igniter unit inside the distributor is loose or corroded. It could also be a bad igniter unit, blue wire, or tach.

 

I don't think so because the cruise dies also and the cruise gets its signal directly from the ecu

 

If these were the problems wouldn't it run bad too? It keeps running the same when this happens.

If it were the tach then why would the cruise die at the same time?

 

I'm not sure if this is it or not, but maybe the speed sensor?

 

Not necessarily. The part of the ICM that sends the tach signal could specifically be bad. Also check the blue wire.

The cruise relies on the VSS signal not the tach signal.

 

Actually cruise uses both vss and rpm. This is an awd wagovan chassis that didn't come with cruise. I added factory cruise and I know for this year it uses both.

 

I stand corrected. You are right. CC uses both VSS and tach signal inputs.