Idle Problem, Needs Help....:(

[chromasupra]

Hi Supra lovers, I do have a problem about surging idle. When my idle speed drops down below 750rpm, it starts surging. As if it's going to die, this happened after the rebuild. Timing is at 10deg it idles @750 if it ever idle, fuel is @28psi again on idle if it ever. Please help!!! Thanks.

 

[smagnotta]

2 things I think your problem can be:

1- ISC - Idle Speed Control
2- TPS - Throttle Position Sensor

The MK3 will "surge" if you unplug the ISC. Perhaps yours is unplugged or malfunctioning? Use a multimeter to check it as per the TSRM.

Another question to pose out there: is 28 PSI the stock PSI setting or is it 38 PSI? I forget as I have an AFPR set at 42 PSI due to the Lexus/550 mod.

I see you have the Aeromotive AFPR in your pic as I do -- if you have the Lexus/550 setup like me I think that 28 PSI is way too low...when I had it that low it was running lean. Every car's setup is different so this too is a guess.

You mention the idle is at 750 RPM. For the turbo my 87 manual says 650 RPM and the NA 750 RPM. Isn't 750 RPM just a little high for the turbo or is it OK depending on your setup?

When modifying the stock setup I guess as long as it runs 14.7 on the A/F ratio who cares what the settings are at...

 

[chromasupra]

I will double check that tonight when I get home early enough, Im not sure if that ISC is working but when the AC is on...idle goes up. TPS, that might be a factor...

28 psi with vacuum hose connected as per stock is 23-30psi, when I raise my fuel pressure...car runs too rich. I can even smell it, but then again I don't have a CAT. I will check and see if the fuel regulator vacuum valve thingy works or maybe there's a vacuum leak somewhere, I don't really know. Would a coil or maybe a knock sensor have something to do with my problem?
Do you think I should set my fuel pressure up? 550cc and that LEXUS AFM plus intake and Q45TB....
Do you know where I can find a gear ratio chart for MA70?

Thanks and Happy Boosting!!!


Oh yeah, it only stabilize @750rpms. Anything lower than that, it surges.
I also heard a slight misfire, Im just running out of clues. huhuhu

 

[smagnotta]

550cc and Lexus -- you better set the fuel pressure to more like 38 to 44 PSI. You are definitely running lean. 28 PSI and I had the same setup and I was running pretty lean. Can you check the Vf and E1 pins on the diagnostic port for the lean vs. rich voltages? Do you know how to do that?

The coil pack - probably not the problem but you can check it with a multimeter. You can check the volts and ohms as per the online TSRM Toyota Supra manual.

 

[chromasupra]

I don't really know how to check that, do you know where I could find pin outs for that or if you can help out.... I tried calibrating my TPS, I did it through my SAFC... There's a throttle sensor included with that, I dont really know if that's the right way of doing it. How do you calibrate your TPS? I do have another ISC, I will replace it when I get a chance maybe tonight. I will let you know, thanks for the help bro.

 

[smagnotta]

It is called the diagnostics port. It is a little black plastic box. I think there are 8 pins in there. They are marked on the other side of the cover when you open it up. I think the work "Diagnostics" is even written on the cover. It is small - it is right by the battery on the driver's side. It has a lid. You need to pop it open and then you will see what I mean.

 

[chromasupra]

I know and I've seen that diagnostic port. I even jump 2 terminals when I check my timing, you're saying that it's I should take a closer look. I should do that ha, maybe this weekend. Is that a pic of the new supra? Wowow, Thanks bro...

 

[smagnotta]

Yes that is a computer generated image of the MK5. Who knows if it will ever see production as Toyota has been dragging its feet. I think they are locked on Lexus and we won't see a Supra again. :cry:

Yes go to that diagnostic port and you will see Vf and E1. Put a voltmeter/multimeter on it and set volts to 20 on your unit. Then put the red and black on VF and E1. If you see a negative number, you've got it backwards.

If you see 5.00 you are running lean, 0.00 is running rich and 2.50 is stochimetric (just right)...If you see 3.50 you are still on the lean side.

I think you will see 5.00 or 3.50 is my guess. :burnout: