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post #1 of 15 (permalink) Old 01-17-2013, 04:19 PM Thread Starter
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Low RPM at Idle- Dimming Lights

Hey guys. Me again. Thought I'd ask as you've been very helpful recently. Cobalt '05 with 148K on it.

A few weeks ago I brought it in due to bad idles and the car stalling a few times at lights or when slowing down. The mechanics caught no codes but did clean out a very dirty throttle body. For the past 2 weeks it's been running great: idling about 750 RPM.

Today, the RPMs dipped to well below 500 as I slowed to my driveway and the lights (headlights and gauges inside) dimmed. Since it's not the throttle body, could it be the MAF sensor? (I've been reading about this problem).

I am also going in to get a new fuel filter next week to be careful. Any ideas are greatly appreciated guys- this car is driving me crazy these past few months!
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post #2 of 15 (permalink) Old 01-17-2013, 04:25 PM
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post #3 of 15 (permalink) Old 01-17-2013, 04:29 PM Thread Starter
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post #4 of 15 (permalink) Old 01-17-2013, 05:09 PM
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Just throwing this out there but if your lights are dimming I would get your alternator and battery checked. Make sure the charging system is working properly. If you have no juice your voltage for the ignition will be weak. I may be misleading you but it's just a thought.
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post #5 of 15 (permalink) Old 01-17-2013, 08:07 PM
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Like blazer said, easy stuff first (assuming you haven't looked at these already). Check your battery and alternator (corrosion, connections, belt tension, etc.) What problem have you been reading about with the MAF?

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post #6 of 15 (permalink) Old 01-17-2013, 08:26 PM
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Engine idling low is the cause of lights dimming and not the other way around. Wish I had more details on the symtoms. But I'm going to go with one of the rev-up sensors not working properly here. You have an 05 so a PCM. Do your brake lights work? It could be the PCM not telling the TCM that you're applying the brakes and therefore not releasing the torque converter and bogging down the engine. MAF is always a possibility though but that is really hard to diagnose from here, plus MAF will usually set a code if it works that bad.

Could also be moisture coming through the fuel line at the wrong time of your trip.

Just need more detail of symptoms and what's been done on it lately that might be the real cause.

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post #7 of 15 (permalink) Old 01-18-2013, 07:34 AM
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Quote:
Originally Posted by Coby7 View Post
Engine idling low is the cause of lights dimming and not the other way around. Wish I had more details on the symtoms. But I'm going to go with one of the rev-up sensors not working properly here. You have an 05 so a PCM. Do your brake lights work? It could be the PCM not telling the TCM that you're applying the brakes and therefore not releasing the torque converter and bogging down the engine. MAF is always a possibility though but that is really hard to diagnose from here, plus MAF will usually set a code if it works that bad.

Could also be moisture coming through the fuel line at the wrong time of your trip.

Just need more detail of symptoms and what's been done on it lately that might be the real cause.
This. And a lot of times, the MAF will not only throw a code, but if it was THAT dirty, you would notice it when you open your air filter box where the MAF is located. You can still clean it though, it never hurts to clean it, just use MAF cleaner specifically.

I'm still going to go with Coby on this one, if it has been running fine and just one time it fell like that then it could just be a little water in the fuel. Run some Sea Foam through your tank, that will help clean a lot of the Impurities out of your fuel system. Your car can run like you said if you have injectors sticking and putting WAY too much fuel in your cylinders (flooding out).

A little more info would be VERY helpful in this situation though.

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Mods - Injen CAI, CIA MAF Relocate CP's, Dejon FMIC,
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Mods - 5in TBE, Boost Elbow set to 28psi, Adjusted fuel pump, Open Turbo.

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post #8 of 15 (permalink) Old 01-18-2013, 03:45 PM Thread Starter
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Thanks guys. Yea, it appears to have been only the one incident, and the tank was nearing a quarter. (I've kept it half full at least until this time !)

the air up here in Toronto is freezing too (-15C this week) so I will go with your thoughts on this and assume it's moisture.

Thanks for the tip on the Sea Foam. I'll give it a try.

Oh, and yea the brake lights work Coby, so I hope we've narrowed this down :p

Thanks again!
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post #9 of 15 (permalink) Old 01-18-2013, 04:00 PM
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I live by Sea Foam in all my vehicles. so from a professional and personal opinion, it works fabulously.

'09 SS/TC - Stolen
Mods - Injen CAI, CIA MAF Relocate CP's, Dejon FMIC,
Custom 3" DP, 3" Exhaust, GT3076R, Pioneer AVH-4100DVD, Hurst STS, ZZP triple pod, Autometer Cobalt boost/DPIC/WB gauges, Nitto NT05 245/40/18's, H&R Springs, 80:20 Meth Spray
Future - KSport Kontrol Pro Coilovers, 10% Tint, FMIC spray
538whp/501wtq @38 psi on meth and 93 oct on stock ish motor


06 EVO IX MR/SE - Sold
Mods - *Updated 10/6/13* AEM TRUboost EBC, 4in custom TBE, SD dual 93/e85 tune, ETS 4in Race Core FMIC, Dual Aeromotive 400lph Fuel Pumps, T4 Tubular Manifold w/ dual WG's, FP Super99HTZ DBB Turbo, GSC 274 mivec cams, ARP headstuds/rod studs, FIC 2150cc Injectors, Aeromotive FPR, Aeromotive Fuel Rail, catch can, Mini Battery Kit, Slim Coolant Fan, Kiggly Racing high pressure valve Springs/Titanium Retainers, Supertech Stainless Steel Valves, Dual VTA Tial 44mm WG's, 4g64 Stroker Manley Pistons, 155mm 2.4 LR Manley Turbo Plus I Beam Rods with ARP 625 Studs, 100mm forged non-billet Manley Crankshaft, Full H/E PNP with Port Matching, Kiggly Racing Girdle, Dual Tial 50mm BOV's, Excedy Triple Disc Carbon HD Clutch, AEM EMS

'95 Ram 2500 Diesel
Mods - 5in TBE, Boost Elbow set to 28psi, Adjusted fuel pump, Open Turbo.

Future Mods- Super Street Clutch (rated @1400ftlbs tq), 67mm turbo, 160lb valve springs, added timing, tubular exhaust manifold, larger injectors, possible 6 spd swap.


Master ASE Certified Gasoline/Diesel Technician since 2004

Speed Junkies Social Group

Yourcobalt Official Facebook Page!

Syndicate of Tuners Official Page! Up and going again as of 1/11/13

Click here to PM me if you have questions or issues!
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post #10 of 15 (permalink) Old 01-18-2013, 06:44 PM
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Re: Low RPM at Idle- Dimming Lights

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