when checking the ohms and voltage on a vehicle, do you go by DCV or ACV or DCmA ?

Question

I`m needing to check the IAC and the TPS on my 94 gmc 1500. I think my EGR is OK and all my vacuums look in tack. When my engine is under a load after warm up. It stumbles when I have it in gear or run the ac. I can place back in neutral and it goes away. Going down the hwy it runs fine.

Answer 1

Always DC. Usually V (volts).
You need to look at a service manual if you are going to check any sensors because they usually want to know ohms
to see if the sensor is operating correctly.

Answer 2

Before you get too deep in component testing and replacement, go here------->

http://autorepair.about.com/library/ts/obd-i/bl-dtcs-51a.htm?once=true&

…and scroll down below the chart for a discussion of retrieving the Diagnostic Trouble Codes. It is very simple, non-intrusive, harmless and only requires a paperclip.
IF… you retrieve code(s), proceed with diagnostics for the system or circuit the code indicates. Don't waste your time checking resistance and voltages where there is no code.
Refer to a QUALITY repair manual or factory SHOP manual (library?) for proper procedures.
Run the diagnostics first, THEN proceed to the necessary repairs. If you follow this order, you will only need to repair it once, and you will repair the problem and the sympton as well.
Check also for a coked up idle air passage (won't throw a code) Also check the plastic line from the vacuum source to the MAP sensor very closely.

Happy Motoring

Answer 3

I've been experiencing periods of lousy idling also, and I'll tell you what I suspect (but can't prove it).

I think the methanol or alcohol they're mixing with the gasoline doesn't stay in solution, because I notice that it's toward the last quarter tank that my car begins to idle badly, but when put in fresh gas, it runs fine again.

I think there's a higher concentration of alcohol (methanol) that rises above the gasoline, and it needs higher compression to run well, so it runs lousy on that last quarter tank.

Well, there's my bush-league opinion, for what it's worth.
.

Answer 4

You can get a reading on dc or ac, but it's actually a variable width pulse coming from those things, and you'd need a meter that reads that in duty cycle to be accurate.

Answer 5

Cars are DC, houses are AC. Too bad, I work electronics, not engine repair or I'd help more.

Answer 6

DCV. Vehicles have a 12VDC power system. When checking resistance, you will use ohms.