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Old 07-03-2015, 09:46 AM   #1
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Default 1990 Miata wont run after supercharger taken off!

I have a 1990 miata, that had a JRSC (M45) and i removed it to install my new turbo setup. after remving the supercharger, the car runs absolutely awful. It will not hold a idle, and if you put it to the floor it will go up to 3k and back down to 2k constantly. I replaced all the vaccuum Lines one from lower throttle body one from valve cover ventilation and one from my air fuel pressure regulator. Any help would be awesome! thanks!
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Old 07-03-2015, 10:49 AM   #2
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pics of engine bay and plumbing.
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Old 07-03-2015, 12:10 PM   #3
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Need info on engine/fuel management as well.
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Old 07-03-2015, 04:40 PM   #4
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Running a voodoo box. Timing is retarded to 8 degrees. Stock internals. Holding it to the floor just goes to 2500 rpm now and back down to to. Then back up again to 2500. Could this be a bad throttle position sensor? As the case did crack off it on accident.



When supercharger was on.(jrsc)











Attached Thumbnails
1990 Miata wont run after supercharger taken off!-80-image_7fb6248c9a0ef5eab512d410a68d0947b2292f7c.jpg   1990 Miata wont run after supercharger taken off!-80-image_5eeef186c302752d7db973a072338cab03d624a6.jpg   1990 Miata wont run after supercharger taken off!-80-image_521145fd22d54c9f243b61e44f3242f79323c6bf.jpg   1990 Miata wont run after supercharger taken off!-80-image_4fcb93ab2fd407e1d9056fbdc96f12b135405097.jpg   1990 Miata wont run after supercharger taken off!-80-image_3a28a9a087dcbe9a622d1eb6a23716c8570dcd9b.jpg  


Last edited by Ernie Brouillard; 07-03-2015 at 04:46 PM. Reason: Incomplete
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Old 07-03-2015, 06:38 PM   #5
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Try unplugging the throttle sensor. On the 1.6 cars, it's just an on-off-on switch, and disconnecting it will simulate mid-throttle. Eg: the car will run 95% fine without it.
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Old 07-03-2015, 07:15 PM   #6
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Did you move the voodoo map pick-up to after the throttle when you moved the TB?

Did you make any wiring changes? Did you temove the tps extension that is needed to relocate the TB for the JRSC?
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Old 07-03-2015, 09:55 PM   #7
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took off the sensor. now iot freely revs to redline. but idle sticks at 3k no matter how i adjust the idle screw.
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Old 07-03-2015, 10:09 PM   #8
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Is there slack in the trottle cable?

Does the throttle cable cam close all the way to the stop?
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Old 07-03-2015, 10:10 PM   #9
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BTW, double check the wiring on the TPS cable if you rewired it. If you wite it wrong you can short the 12v with the WOT switch.
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Old 07-04-2015, 10:15 AM   #10
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Ignorance is not bliss. But if it was I would be one hell of a relaxed person. I'll go check the throttle cable tension in a few. Thank you guys!
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Old 07-04-2015, 10:53 AM   #11
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and that long as line with the check valve is the idle valve inlet?
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Old 07-04-2015, 11:52 AM   #12
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The big ol thick one with that check valve connects to the throttle body yes.
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Old 07-04-2015, 02:01 PM   #13
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Well, adjusting the throttle cable itself did nothing. it will idle high as **** for about 10 seconds and then go down to normal. at normal idle it sounds like **** though. take into consideration i have a hallowed cat. I checked the plugs and they seemed to be ok. any input is appreciated!
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Old 07-04-2015, 02:15 PM   #14
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Quote:
Originally Posted by Ernie Brouillard View Post
took off the sensor. now iot freely revs to redline. but idle sticks at 3k no matter how i adjust the idle screw.
This post and the last post are misleading. Please clarify what is happening. Note any changes since the original post.

Keep in mind that when solving problems that involve several interactions and variables, elimination of a potential cause is of great value. Additionally, ANY change (good or bad) that can be associated to a single point change needs to be noted.

Solving HW and SW problems from this side of a screen is very difficult if the observations from the experiments are not reported clearly and completely. Magic bullets rarely exist.
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Old 07-04-2015, 02:27 PM   #15
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The only thing that can make idle go up like that is the idle valve or a large vacuum leak.


when you unplugged the AFM, did you use a screwdriver and remove screws?

where are the vacuum lines going? you have tees off the TB and extra lines going to random places...
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Old 07-04-2015, 03:26 PM   #16
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No i didnt remove them. that ruins it doesnt it? haha. well theres one tee thats going to my voodoo box. and boost gauge. OK, I unplugged the tps and now it idles at 3k and will go down to regular idle eventually after a few seconds. it will rev all the way to redline just fine unlike when the tps was still plugged in.
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Old 07-05-2015, 02:18 AM   #17
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So, for the TPS... Did you remove the spliced in extension when you relocated the TB?

If not, or if you did it correctly the sensor is most likely shucked and needs to be replaced.

Unplug the IAC, what does the car do?

I haven't ever worked on a miata with cruise control. Is it possible that could be causing the problem?
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Old 07-05-2015, 11:42 AM   #18
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1: It seems like we've established that the TPS may have been at fault in the original problem; the inability to rev beyond 3,000 RPM. It suggests that the IDL terminal of the TPS was faulted to ground. This can be verified by testing it with a multimeter, as per the following procedure (don't worry about the feeler gauge for the moment, just test it closed, midway open, and fully open):






2: Now that the TPS is removed from the circuit, a new problem surfaces, or perhaps an existing problem becomes more clearly defined; that the engine won't idle properly. We must determine which.

3: Post # 13 seems to contradict post #7, by adding the following information: "it will idle high as **** for about 10 seconds and then go down to normal. at normal idle it sounds like **** though."

4: I posit the following test:
Re-connect the TPS. Does the engine now idle normally? Does the problem of not being able to rev past 3,000 RPM come back? If so, you have definitely diagnosed a bad TPS. If not, report back on exactly what happened



Also, be careful with the two screws which hold the TPS in place. Instead of metal, they are made of a soft French cheese and the heads will strip very easily.
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Old 07-10-2015, 09:32 PM   #19
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Alright, installed a new TPS. didnt seem to make any sort of change. still running like **** and misfiring at 800rpm idle, tap the gas and it goes up immediatly to 3krpm and stays there. comes down eventually but it takes a bit. could the misfire(y) feeling at idle be because my timing is retarded to 8 degrees and im no longer running boost?
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Old 07-10-2015, 10:15 PM   #20
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Unlikely.

Try the other suggestions and answer the other questions in this thread.
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