Bad IAC? (Page 2/3)
Stricken SEP 13, 04:48 PM

quote
Originally posted by Blacktree:

IMO, it's best to check after the car's been sitting overnight. Because then, both sensors will be at ambient temperature.



The car's been sitting for a couple of hours with the lid open. The IAT is reading 670ohms, and it's only 88* outside. It appears to be original as I can't break it loose, so I have it soaking in penetrating oil right now. I think that may be the culprit, or at least one of them.

The coolant sensor is reading 470*. The engine is still hot, but not scalding hot, so that seems about right.
Gall757 SEP 13, 04:51 PM

quote
Originally posted by Stricken:


The coolant sensor is reading 470*. The engine is still hot, but not scalding hot, so that seems about right.



Are you joking? Perhaps you meant 470 ohms?

[This message has been edited by Gall757 (edited 09-13-2020).]

Blacktree SEP 13, 05:59 PM
470 Ohms would correspond to just under 160*F, so yeah. But that intake temp sensor is WAY off.

Edit to add: These old computer setups are pretty crude. For example, the intake and coolant temp sensors don't set a trouble code unless there's a dead short or an open circuit. So the sensor can go bad and the ECM doesn't know it.

[This message has been edited by Blacktree (edited 09-13-2020).]

Stricken SEP 13, 06:17 PM

quote
Originally posted by Gall757:


Are you joking? Perhaps you meant 470 ohms?




Ha, yes 470 ohms, not degrees.
Stricken SEP 13, 06:25 PM

quote
Originally posted by Blacktree:

470 Ohms would correspond to just under 160*F, so yeah. But that intake temp sensor is WAY off.

Edit to add: These old computer setups are pretty crude. For example, the intake and coolant temp sensors don't set a trouble code unless there's a dead short or an open circuit. So the sensor can go bad and the ECM doesn't know it.




I found both on Amazon for $8 and $12, so I ordered both arriving tomorrow. I'll replace the IAT and send the coolant sensor back if that improves things.

Stricken SEP 14, 06:30 PM
I replaced the IAT, and that made no difference. Autozone had the IAC in stock, so I replaced that, made no difference, and returned it. I discovered that there was a code 34 on the ECM, but no SES light. I tested the MAP with a vacuum pump, and it seemed OK. Autozone had the MAP in stock, so I replaced that. With the new MAP, the idle seems better, but not good. It hasn't died with the AC on yet, but it bounces all over between 700-1400rpm.

My only other thoughts are the EGR is doing something weird or the O2 sensor maybe?
Patrick SEP 14, 07:44 PM

quote
Originally posted by Stricken:

...it has consistent ~38psi fuel pressure at idle and increases when I blip the throttle.



How quickly does the fuel pressure drop when the pump is stopped? A rapid drop may indicate a leaking injector or two.
Stricken SEP 14, 08:20 PM

quote
Originally posted by Patrick:

How quickly does the fuel pressure drop when the pump is stopped? A rapid drop may indicate a leaking injector or two.



I removed the schrader at one point, and fuel squirted out initially. I took that as a sign pressure wasn't leaking down very fast, but maybe it was leaking low enough to just stop leaking...
Stricken SEP 14, 08:23 PM
The EGR diaphragm isn't moving nor is it getting a vacuum signal to open, so I don't think the EGR is the problem.
Patrick SEP 14, 08:27 PM

quote
Originally posted by Stricken:

I removed the schrader at one point, and fuel squirted out initially. I took that as a sign pressure wasn't leaking down very fast, but maybe it was leaking low enough to just stop leaking...



In other words, you don't know. See what your fuel pressure tester tells you!

And I have no idea what your response was to my question about checking the TPS.


quote
Originally posted by Stricken:

I inserted some safety wire into the middle wire of the TPS connector and checked that against ground.


[This message has been edited by Patrick (edited 09-14-2020).]