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Old 04-21-2009, 08:07 AM   #1
Join Date: Apr 2009
Location: Chico, CA
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Question RPM drops down every 5 seconds

Hello all... sorry if my post becomes really long!

I just got my hands on a 1989 Toyota Supra Turbo M/T. The previous owner (a relative of mine) had just completed a JDM engine swap due to a bhg on the original engine @ 170k miles.

When the previous owner got the car, it had no EGR valve installed and it had the injectors upgraded to 550cc along with an Apexi-RCVR boost controller installed. When putting in the JDM engine, he kept the 550cc injectors and the Apexi-RCVR boost controller setup.

With that information out of the way, here are a few problems I'm seeing with the car and I'm hoping you can help me out. I am a newbie to the car, however I've been through the TSRM daily numerious times so I'm pretty familiar with certain areas.

Problem 1) The check engine light does not report any trouble, however when reading existing codes I always get 51 (switch circuitry). All of the hunder-the-hood A/C components are removed from the vehcile, so i've been assuming this code is referring to the missing A/C amplifier. Does this sound correct?

Problem 2) The engine seems to be missing now and then, more so at higher RPMs (duh) and so far the injectors, plugs, wires, etc seem alright. What else should I check?

Problem 3) When driving, i've found that sometimes the turbo boost will kick in just fine, and other times it will start to kick in but then start to cut out during the boosting. It happens probably about 50% of the time. Any suggestions on what this might be? Possibly due to Problem 2 above?

Problem 4) Once the car has warmed up, if I hold my foot on the gas pedal (or manually move the throttle bar under the hood) and hold the RPM at 2500 to 2800 steady, the RPMs seem to drop down to just about 1000 every 5 seconds. The Apexi-RCVR boost controller shows the injector percentage, and it shows an average of 4% to 5% while holding the RPM steady, and when the RPM drops, this percentage drops to 1% or 0% so it seems it's the ECU that is choosing to cut out, but why? No check engine light, and no codes other then the 51 mentioned above are read out during a diagonstics check. Does anyone have any ideas what could cause this?

Problem 5) My father, who was a mechanic for many years in the past, told me the car seems to be running too ruch and is misfiring (problem #2 above). He suggested that I check to make sure the O2 sensor is working properly, and I will be going through the TSRM troubleshooting steps for this tomorrow, however I wanted to ask if anyone could suggest anything else I might want to check?

Thank you. The forums have been extremely useful, i'm not sure where i'd be at with this car without them!
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