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Randall C
Randall C, ASE Certified Technician
Category: Car
Satisfied Customers: 12803
Experience:  32 years Foreign / Domestic Cars All aspects of Diag and Repair
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Scion TC: Why engine stalls when lights are turned on?

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Engine stalls when lights are turned on? Whenever I turn on the headlight, or turn signal, or press brake, or change gear, car nearly stalls or completely stalls. I can't drive car in this condition. I just got this car (in this condition). The battery that was cracked and leaked acid. So I thought it was just that I needed a new battery. I already did buy a new battery, and it did not help. It might be something unrelated. I don't know. Thank you!

Hello, I am Randall. I have reviewed your question and working on it now.
Sorry for the delay
Kind of hard to say exactly whet the problem is but,, most common? you have a dirty throttle body
They get gummed up over time and the computer can not maintain idle as required when loads are placed on
I would have charging system checked, just to be sure you have 13.8-14.5 volts at the battery, running. Just a check to eliminate as a possible charging problem
I am still thinking dirty throttle body
You need a can of carb cleaner. remove the air intake hose from the throttl e body
Gently spry the bore inside , put hose on, start, rev and blow out. Clean up till say 4-5 times till shiny as shown below
This should eb done once per year
Aside from this? it then need to be on a scanner to see how sensors etc are all performing
Worst case could? need a new throttle body as the idel control is built into it but.. let's not go there , I am leaning to dirty throttle butterfly and throttle body bore


Customer: replied 3 years ago.

Hello again. The battery acid got everywhere, including cables and everywhere. I noticed the cable/connector that is attached to the starter got somewhat damaged. Also, on the starter itself there is a lot of this acid and the connector was covered in the acid. I cleaned it off, but there still seems to be some damage there. Could this play a role? Would a bad starter, or bad starter connection cause a car to stall once running? Or does the starter only become engaged on the initial start-up? Thank you

starter wiring should play no role in stalling. Acid on a componet other than starter wiring yes,, but I can not answer that.
I highly suggest the Throttle body cleaning as this may fix the problem. If not? then inspect all wiring real close at the throttle body as the idel and throttle control arte computer controlled or "fly by wire" damage to wiring at throttle body is possible
Customer: replied 3 years ago.

Well, I was wondering if perhaps It might not be a throttle issue because the problem presents itself when there is an added electrical load, such as turn signal, or turning on headlights. What do you think?

Still clean the throttle body. Gummed up and computer can not react to loads fast enough and causes stalling exactly like you describe. In the shop? this is the very first thing done. Wiring? possible with acid on or near throttle body wiring but.. That is not common at all so I have to tip toe into that one.
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