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Old 11-04-2007, 11:46 PM   #1
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Default After engine transplant, car running like *****.

Actually, it was more like a Miata transplant, because i took my drivetrain and put it in a non-totaled Miata.

Even on the stock computer, when i rev it and hold it around 2k rpm, the car starts surging up and down exactly 250 rpm. It's very precisely rhythmic up and down and will stay that way until i rev past that point (which it doesn't immediately want to do) or let the revs drop.

Also, the car has a severe problem transitioning into boost and bucks like a wild horse at cruising speed.

I have tried:
Checking for vacuum leaks. I get -25 at vacuum, and the vacuum isn't effected much by the surging.

I have checked all my ground points and verified good connectivity of the O2 sensor.

I have hooked up my laptop to the emanage/autotune and confirmed the proper 50% throttle position (O2 sensor voltage) recorded by the Emanage.

Consider that the entire drivetrain was swapped from the old car, from the engine and transmission, the rear end, my fuel pump, Vortech FPR, and my Emanage and autotune. (We're talking months of coming to work on this thing on the weekends.)

After the installation of the Emanage, the problem is still there.

Granted, the only thing i used on the new car was the ECU, and I did reuse my old throttle body even though it might have gotten damaged in the wreck. I'm going to try and change those out first.

Any other suggestions?
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Old 11-04-2007, 11:53 PM   #2
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check your idle valve.
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Old 11-05-2007, 12:39 AM   #3
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i'm thinking that. it could have been damaged in the wreck. that's the valve at the bottom of the throttle body that the question-mark shaped hose attaches to, correct?

Also, I see where that could fix the problem with the 2k rpm issue. I'm hoping the ECU swap will fix the boost transition issue. I found out during the transfer that the original wiring harness had been hacked someone for a Powercard install. Not a big deal, but I need to check all the splices the PO made.

what a colossal PITA this project has been. lol.
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Old 11-05-2007, 09:53 AM   #4
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do you have the old TB assembly? you might wanna try swapping that on.
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Old 11-05-2007, 10:03 AM   #5
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For the transition into boost, recheck (and possibly adjust) the o2 clamp setting on autotune. I got best transition results by setting my 02 clamp to just a little richer than the voltage for 14.7 afr which IIRC was around 0.45v If it's set too rich/lean, you'll get bucking transitioning into boost.

I'd also check the pressure switch to make sure that it's not set to low and that you are jumping into and out of autotune at cruise.
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Old 11-05-2007, 10:07 AM   #6
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Take your TPS setting on the autotune to 55% since you are not using it to pull fuel(in case you have a voltage drop) and try swapping in your old AFM.

Did you install the ground strap at the rear of the motor below the brake booster?
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Old 11-05-2007, 10:56 AM   #7
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Well since it gets dark at 5:30 now (god I had this time of year), I probably won't have a chance to change out the throttle body until the weekend. I'm going to attempt the TPS setting change this evening. I'll let y'all know.

BTW, I'm using my old AFM and the ground strap is firmly secured.
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Old 11-05-2007, 08:53 PM   #8
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The TPS sensor may be out of adjustment... I had a similar problem when mine was off by about 10 degrees of rotation.
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Old 11-10-2007, 09:53 PM   #9
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Well, I replaced the entire throttle body with a spare and the car idles and runs through the revs fine now. However, my transition into boost is still pretty rough and I start to sputter at high rpm's in boost, causing an "Oh ****!" reaction. It's entirely possible the injectors may be varnished, as the car sat unused for almost 8 months. I also haven't had a chance to adjust the voltage on the autotune, which i suspect is the cause of my bucking/tip-in problem.

I just wonder what is causing the stumble at high revs.
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