Need help with idle

[Bigbertha78]

So as I'm driving when I come up to a stop sign or stop light the trucks RPMs dive down to around 300, at night the lights go dim, oil pressure, and volts both go down a bit. Couple seconds later the RPMs go back to normal. Last night was the first time I noticed it doing it when I went from Park to Drive but only once. New air filter installed, cleaned MAF sensor, and throttle body. No codes have popped up nor have I gotten an engine light. I have no idea where to go next, any help will be appreciated. 2004 Tahoe Z71 5.3L with 134,000 miles. Truck has progressively gotten worse over the last few months.

 

[drakon543]

Well first since i ask everytime when i see someone cleaned the maf and tb. Did you use appropriate maf/electronics safe cleaner on the maf and tb. Anything else may possibly damage some of the electronics. Anyway are you using the a/c or the defrost setting while this is happening? Your voltage regulator could be getting weak causing the voltage to dip down for a second but not quite low enough to have the light come on. My other geuss would be your drive by wire throttle contoller is getting weak. The drive by wire tb also have the tps and idle air control built into them. Its possible for only that part to start going bad.

 

[Bigbertha78]

Both parts where cleaned with appropriate cleaner. Also, this is happening under no load, no AIr conditioning on either. Is there any way to test the parts you mentioned above to see if there is a problem?

 

[SLCHOE]

Check your battery and alternator.

If you have a multimeter, hook up both leads to the battery and check voltage as the truck is running. You should have ~14 volts. Battery voltage with the engine off should be ~12.6 Volts.

My thinking is your alternator is about to go or has already gone kaput.

 

[Tibo77]

Any chance you may have moved the butterflies on the throttle body when you cleaned it?

 

[Bigbertha78]

So I took the truck in to have the alternator tested and you guys were right. Alternator is going bad. He hooked up the multimeter with the truck running and it had 13.97 volts for about a minute and then it would not even register anything. About 20 seconds later it goes back to 13.97 and back to nothing. Guess I'll be looking for a new alternator.

 

[SLCHOE]

Yup. When you lose voltage on these trucks, the ECM loses voltage. If the ECM voltages drops low enough, the sensors and solenoids it supplies voltage with don't have enough to work properly. Thus the engine performance issues (idling low).