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Doug C.
Doug C., ASE Certified Technician
Category: Car
Satisfied Customers: 6297
Experience:  16 years automotive and OTR repair including specialized training from Toyota and Mitsubishi
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Mitisubshi 3000GT SL: Hi, my grandson has a 1993 Mitsubishi

Customer Question

Hi, my grandson has a 1993 Mitsubishi 3000GT SL. It has 114,000 miles on it. it runs very good. The SRS light always stayed on. After reviewing this with the 3000GT forum, we removed the 2 bulbs in the dash so the light would not show any longer. The removal of the dash was pretty straight forward and easy to do. However, after this we started to have a problem.

When the car is running and A/C is shut OFF the car stalls. Upon restart it starts right up and turning the A/c ON is no problem, until we shut the A/C Off again. Car stalls and will easily restart. If the car is parked and we turn the A/C off the idle drops but doesn"t shut off until we hit the gas. How do we fix this? Did we do something wrong with the dash cluster?
Submitted: 1 year ago.
Category: Car
Expert:  Doug C. replied 1 year ago.
Hi,

Was the battery disconnected during this process?

When was the last time the throttle body was serviced?
Customer: replied 1 year ago.

The battery was not disconnected. The car had a complete service just before we purchased it. New timing belt, plugs and wires, etc. I will have to look at the receipt to see of the throttle body was cleaned.

Expert:  Doug C. replied 1 year ago.
Thanks.

When the vehicle is idling and you turn off the AC, if you very gently apply the gas pedal does it still stall?
Customer: replied 1 year ago.

Yes..but once it stalls and we restart it starts right back up again.

Expert:  Doug C. replied 1 year ago.
Sorry about the delay.

So even slightly applying the throttle it will still stall, but when the AC is on it is OK.

What is your idle speed warmed up, AC on and AC off?
Customer: replied 1 year ago.

When the AC is on everything works OK. Car Idles nice runs fine. Only it shuts down when the ac is turned off.


Not sure what the idle speed is with ac on vs ac off. I will look at that tonight. Can I get back to you then?

Expert:  Doug C. replied 1 year ago.
That is no problem.

I am here through the evening, just post when you have some idle speeds for me and we will continue from there.
Make sure the engine is warmed up when you get the idle speeds for me. Also think if there are any other symptoms (even if seemingly unrelated) that you haven't mentioned.
Customer: replied 1 year ago.

Ok... here's the scoop. With the ac on rpm =(NNN) NNN-NNNNwith the ac off the rpm = 600-700.


We have not noticed anything else unusual. We have only had the car a week though. The ac has been on all te time. Just got cool here yesterday so the ac was shut off.

Customer: replied 1 year ago.

Ok... here's the scoop. With the ac on rpm =(NNN) NNN-NNNNwith the ac off the rpm = 600-700.


 


We have not noticed anything else unusual. We have only had the car a week though. The ac has been on all the time. Just got cool here yesterday so the ac was shut off.

Expert:  Doug C. replied 1 year ago.
Hmm.

The computer is adjusting properly for the AC so that is out. The AC off idle is a little low, but not enough to stall it by any means.
This has never happened before since you purchased it right?
If you idle the engine, but keep your foot slightly on the gas to bring it up maybe 200 rpm or so, then turn off the AC does the engine still stall when you give it more gas?
Customer: replied 1 year ago.

Hi Doug, here's what we did. Double checked the ac off idle and it is about 600-700 rpm. We turned on the ac and the rpms went to 1200 and almost immediately down to 1000. Put our foot on the gas increasing the rpm to about 1200 - 1300 rpm, keeping our foot on the gas,shut off the ac and the rpms droped to 200 - 300. It did not stall. We then stepped on the gas a bit and the engine did not stall and settled out at about 600 rpms.


Again we have only had the car a week and the ac has been on the whole time. Just got cool last night and the problem started.

Expert:  Doug C. replied 1 year ago.
Thanks.

This is pretty interesting.... so with the gas pedal partially applied and you turn the AC off, the idle actually drops lower than if you had not touched the gas pedal, hitting 200-300 before coming back up.

Do you have a test meter and some familiarity with it?
Customer: replied 1 year ago.

If we had not raised the rpms by 200-300 the car would have stalled.


 


Yes I have volt/ohm meter and I am not an expert but can use it. I have both an anolog and a digital meter.

Expert:  Doug C. replied 1 year ago.
Ah thank you, XXXXX XXXXX

There are two things I'm immediately concerned with. The first is the TPS output, the second the actual idle speed. After those I can't see anything here but relative long shots (timing belt off a tooth etc).

So lets start by testing our TPS out.
Here is a reference diagram so you can see what we are working with, the pin outs, etc.
graphic
Also for ease of identification of the wires, they are colored as follows:
1 Green/Yellow
2 Brown/Red
3 Yellow/Red
4 Black


Get your analog volt meter handy and perform the following checks:
Voltage on pin 1 with key on and sensor UNplugged
Ground on pin 4 with sensor UNplugged (you can connect your volt meter to pin 4 and the battery positive, or use your digital meter to read resistance to ground)

Get your digital meter and set it to ohms and measure the resistance between pin 1 and 4 on the sensor


The next test is a bit odd... you really need an analog ohm meter for it. Hopefully yours does this, if not I will figure a work around.
Connect the ohm meter between pins 2 and 4 and get a reading. Slowly twist open the throttle while watching the reading. We want to see a smooth, linear change in resistance... no jumps, no bouncing around, no flat spots where there is none/full resistance etc.


Let me know the tests on all of those as accurately as you can, then we will move on to the throttle close switch test.
Customer: replied 1 year ago.

OK..we will try this tomorrow as we have an appointment tonight. I will let you know how we make out....thanks, Carl

Expert:  Doug C. replied 1 year ago.
No problem
Customer: replied 1 year ago.

Hi Doug, sorry for the delay in getting back to you. We had a family emergency tha took priority. We did have a few mins so we decide to clean the throttle body. After the cleaning the problem went away. I think its fixed, though the throttle bodu didn't look that bad. Thsnks for your help. We'll keep the test you sent us should it happen again.

Expert:  Doug C. replied 1 year ago.
No problem at all; health comes before cars of course.

Hopefully that squares it away; it certainly seemed like that from the description, why I had asked about the throttle service history.

If the problem returns and we need to dig deeper, you have some steps already and we can continue from there as needed. Hopefully this will be the last of it though.
Doug C., ASE Certified Technician
Category: Car
Satisfied Customers: 6297
Experience: 16 years automotive and OTR repair including specialized training from Toyota and Mitsubishi
Doug C. and other Car Specialists are ready to help you
Customer: replied 1 year ago.

Doug, all is working well...Thanks, Carl

Expert:  Doug C. replied 1 year ago.
Fantastic, thanks for the follow up. Have a great day!

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