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rpmdiag
rpmdiag, Tech and Instructor
Category: Mitsubishi
Satisfied Customers: 6847
Experience:  Since 1975
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Engine stalls from idle when giving pedal from idle, No

Customer Question

Engine stalls from idle when giving pedal from idle
JA: Is the check engine light on? Does the car stall at idle or when driving?
Customer: No light. Only when starting off idle
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: Yes. Changed fuel filter , tune up etc.
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 3 months ago.
Category: Mitsubishi
Expert:  rpmdiag replied 3 months ago.

Hi, welcome to Just Answer. I’m Ron and I’ll be helping you
today.
Before we get started though, Please understand that I don't know
your skill level or tools you have to assist us. Also understand that
I can't see, smell, hear, or touch the vehicle either, so patience is
appreciated. JA is a great Q/A site, but it does NOT replace a
repair shop.
My goal is to make you happy and get a great rating in return for
my time. Sometimes I have to give you bad news that I know you
didn’t want to hear, so please don’t shoot the messenger.

The most common cause for this is a bad TP sensor located on the throttle body. It can be tested with a scope for confirmation.

Thanks, Ron

Customer: replied 3 months ago.

OK, I am a full time mechanic, just never worked on one of these. Car idles and runs at cruise perfectly, but when giving it strong pedal from an idle it bogs and stalls. Fuel pressure is 40 psi at idle and 50 psi when doing a snap throttle. Fuel filter, plugs, wires etc all done. Now, here is the interesting part. When I disconnect the MAF connector, the bog goes away and everything is perfect. Problem is that since the MAF and TPS share circuits and I don't have a good handle on the schematic, I'm not sure if it's the MAF or TPS causing the issue.

Expert:  rpmdiag replied 3 months ago.

Ah, thanks for the info. I would also check the MAF signal as well. It can be either. You can only test this with a scope, nothing else has a fast enough capture rate.

See attachments.

Thanks again and please remember to rate me 5 starts and keep this link in case you need me again later on

Ron

Customer: replied 3 months ago.

Thank you Ron. I have scopes in the shop, I just don't have a schematic for either the MAF or TPS for scope hook up.

Expert:  rpmdiag replied 3 months ago.

Okay, check the signal return for both parts and the ground. NOT the feed voltages.

Thanks you too.

Ron

Customer: replied 3 months ago.

Would you tell me which wires - are the signal returns or a schematic if you have one. Thank you

Expert:  rpmdiag replied 3 months ago.

Don't have one in front of me, but here's what you do. get out your DVOM and probe both sensors. The MAF has battery voltage signal and the TP has a 5 volt signal. Ground your black DVOM line to the battery. Now, the other wires are the signal return what the computer sees. You will see about 1/2 volt from the TP and under 5 volts from the MAF. Hope this helps and please remember to rate me:)

Thanks again, Ron

Customer: replied 3 months ago.

Put in a new MAF and a new TPS. Same thing , bogs and stalls art snap throttle. If I disconnect the MAF connector, the bog goes away. Any suggestions?

Here's something interesting. If I connect both the MAF and TPS but disconnect the IAC, the bog also disappears. Somewhere there must be some shared sensor lines but I don't have a good enough schematic to trace.

Expert:  rpmdiag replied 3 months ago.

Okay, then it would have to be a bad computer or the programming.

Ron

Customer: replied 3 months ago.

Ron, thanks for the reply. Traced it down to 3 dead coils on the IAC. Put in a new one and seems fine. Looking at the schematic though, I really don't see why the IAC affects a snap throttle???

Expert:  rpmdiag replied 3 months ago.

It doesn't, has nothing to do with acceleration, only idle.

Thanks again and please remember to rate me 5 stars for my time and keep this link in case you need me again later on.

Ron

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