RPM fluctuation at idle

latief · Post by **latief** » Tue Mar 13, 2007 10:23 am

My RPM seem to fluctuate at idle, this a new thing and i never had this problem before.....
it started a while back, so i changed the coil + wires + plugs.... that did not help.....

my engine also developed a 2nd gear bogdown..... it feels like it hestitates for a second while going from first to second under load.....i feel as if the engine is going to shut off for a second .....other than that, everything runs perfect....

so how do i go about troubleshooting these problems? i have 110,000 on my engine so i guess it could be a big issue, yet it could be a small issue also......

some ideas please......

thanks ,

Post by **racer12306** » Tue Mar 13, 2007 10:39 am

iac maybe

i have to run to class, but when i get back ill look in my fsm for ways to diagnose that.

danielc24 · Post by **danielc24** » Tue Mar 13, 2007 11:25 am

my girlfriends alero has the rpm problem , cant figure it out

Marthby · Post by **Marthby** » Tue Mar 13, 2007 3:32 pm

From the Chilton Repair Manual:

8 Engine lopes while idling or idles erratically
1 Vacuum leakage
2 Leaking EGR (exhaust gas recirculation) Valve
3 Air filter clogged
4 Fuel pump not delivering sufficient fuel to the fuel injection system
5 Leaking head gasket
6 Timing belt and/or pulleys worn
7 Camshaft lobes worn

Personally I would think it's the fuel pump or air filter, maybe the timing belt. 110, 000 miles and the timing belt should have definitely been replaced at least once, it might need to be replaced again?

latief · Post by **latief** » Tue Mar 13, 2007 3:54 pm

timing belt + water pump+tensioner+ seals new at 89,000

what confuses me about all these is the second gear bog-down, which developed recently, i think both symptoms are the part of the same problem.......

Post by **racer12306** » Tue Mar 13, 2007 3:59 pm

i didnt see anything about diagnosing it, just how to replace it.

maybe someone else knows more about the iac

03blackrt · Post by **03blackrt** » Tue Mar 13, 2007 4:10 pm

I had a simular problem twice on my old 2000. First time it was bad plug wires. second time it was a leaking brake booster. maybe that helps. both caused eratic idle. the brake bosster (vaccume leak) cause a noticable bog in first to second gear shift.

Post by **jonnymopar** » Tue Mar 13, 2007 4:52 pm

03+ models have a TSB about this. Reflash the PCM and you're set. Don't know what years people's are here.

turbodudey · Post by **turbodudey** » Tue Mar 13, 2007 5:38 pm

racer12306 wrote:i didnt see anything about diagnosing it, just how to replace it.

maybe someone else knows more about the iac

It's probably not the IAC. The IAC is used to stabilize idle, but when the engine is fully warmed up, it does very little. As far as the 1st to 2nd bog, that's definitly not the IAC, as it is not used at all when the throttle is open.

My guess... vaccum leak.

rich tideswell · Post by **rich tideswell** » Tue Mar 13, 2007 7:16 pm

throttle position sensor, and check the wiring to it. srt-4's had a tsb on this, no logical reason a regular neon wouldnt develope this problem aslo

latief · Post by **latief** » Wed Mar 14, 2007 8:17 am

03blackrt wrote:I had a simular problem twice on my old 2000. First time it was bad plug wires. second time it was a leaking brake booster. maybe that helps. both caused eratic idle. the brake bosster (vaccume leak) cause a noticable bog in first to second gear shift.

i actually think you got it right on !!!......i was looking at the hose that goes from the brake booster to the engine the other day, i saw it was rubbing on the TB (or battery tray, can't remember) correctly) , and i could tell that it needed replacement especially since it would be dangerous if it breaks....that thing was nearly torn all the way from one side although it is relatively new!

does this make sense? i mean will that be a possible reason?

thanks guys,

BRR i need parts for this !!

Edit: I guess i will have to bleed the brakes if i do this, correct?

Post by **racer12306** » Wed Mar 14, 2007 10:10 am

no, its just a vacuum hose.

if you were to disconnect the actual brake lines then you would. but you dont have to do that just to replace the brake booster hose.

you dont even need to bleed the brakes when you do a a simple pad or shoe replacement.

daaboots · Post by **daaboots** » Wed Mar 14, 2007 12:44 pm

latief wrote: what confuses me about all these is the second gear bog-down, which developed recently, i think both symptoms are the part of the same problem.......

My 05 has done the same thing since day 1. I'm assuming you have an ATX. Whenever it shifts gears, the PCM will momentarily shut the engine off for a small portion of time while the ATX shifts gears.... at least thats what the tech at the dealership told me. Sometimes you notice it, sometimes you dont.

latief · Post by **latief** » Wed Mar 14, 2007 1:12 pm

actually mine is MTX, and it has always been great until recently....

i looked again at my brake booster vacuum hose, it is worn in two locations, battery tray and near the TB. the problem is although it is worn, i don't think it is causing the problem since it is not worn all the way through (yet), i mean there is no tear or hole in it yet...at least that i know of..... i will change it anyways... but i guess we could go back to square one on this ......

so what are the components of the vacuum system, in other words what should be checked?
i doubt it would be a head gasket because i have no temp. issues and no oil in the resovour or anything....
if it were a fuel pump / injector issue, wouldn't cause more trouble than just the bog-down and the idle issues?

thanks guys,

Post by **racer12306** » Wed Mar 14, 2007 1:13 pm

a way to check the hose is to spray some carb cleaner on the worn area and if the idle changes then thats your problem. cant remember if the idle will go up or down.

oklamopar · Post by **oklamopar** » Wed Mar 14, 2007 11:29 pm

I had a similar problem and i had a small hole in the tube between the throttle body and intake manifold. fix it and idle came back to normal.
just a thought.

60trim · Post by **60trim** » Wed Mar 14, 2007 11:34 pm

check the rubber/plastic tube that connects the throttle body to the intake manifold. I had a tear on the underside of the tube itself and never saw it. I replaced it when I did my CAI intake back in the day and it solved that problem.

latief · Post by **latief** » Mon Mar 19, 2007 8:31 am

60trim wrote: check the rubber/plastic tube that connects the throttle body to the intake manifold. I had a tear on the underside of the tube itself and never saw it. I replaced it when I did my CAI intake back in the day and it solved that problem.

Thanks, found the problem, the tube itself was completely loose at the intake manifold side .....

it is better now, although i have a slight wistling sound when i hit the gas......

60trim · Post by **60trim** » Wed Mar 21, 2007 12:29 am

Great to see you found to problem...congrats.