RPMs go up and down

[Kulwinder]

Hi Eric
My name is Kulwinder. I have Hyundai Grandeur XG 1999 V6 3.0L Sports
Automatic.
A sudden problem has appeared. From last couple of weeks RPMs go up and down
when I restart my car when it is warmed up. I have to hold the throttle
paddle or engine turns off.
RPMs jump between 800-100 and even completely die. But when I put into
drive/reverse mode they are stable. Drives with no problem. It has new
platinum spark plugs and leads.
It doesn’t happen in morning when I start it first time. RPM stay where they
should be around 2000-1500 then come down. Drives normal.
I don’t have much money so that I let any Machanic to rip me off. It could
be a small thing. That I can fix it myself. Any help please.

Topic

[Glenn]

Hi Kulwinder, A few initial things you may want to check are as follows: a vacuum leak can cause this symptom. Also, the Throttle position sensor or Idle Air Control valve come into play. If you can catch it in the act, you can unplug these components and see if it suddenly changes. Also, it could be as simple as thoroughly cleaning the throttle body with carburetor cleaner. These are a couple ideas for starters. Did the check engine light come on?

[César Morgan]

… I guess I can say that you should (of course) do the testing above, but also, it appears that Hyundai’s most common failure has to do with Fuel delivery systems, it being the Charcoal Canister, fuel injectors, fuel pump… yeah, even the Idle control. By the fact that you just got new spark plugs, we can include as suspects. when doing your testing, make sure that they’re adecuate for your engine.

[Bill]

Could be caused by a stuck open or leaking purge solenoid for the EVAP system. Too many fuel vapors entering the intake manifold on a hot start. Sometimes worse with a full tank of fuel.

[Kulwinder]

Thanks very much guys.
I had cleaned the throttle already following instructions given be Eric The Car Guy. It was very dirty. Then I also cleaned MAF with MAF cleaner. New leads and NGK Platinum spark plugs recommended for my car. Injectors cleaned. Changed the engine oil. It gave back my car lot of power.
This problem just appeared.
I have two amplifiers installed in my car. When I play music loud. I see headlights flicking. Even difference between RPMs. Or exp if I pull up power windows switches together when windows up already. I see RPMs falling. Is my battery playing up or alternator? Can these cause the problem?

[Kulwinder]

How to unplug the components? When on idle? One by one?
Please give more info about this step.
Thanks

[Glenn]

Yes Kulwinder, you would do this when car is idling in park. Basically, when it’s acting up, disconnect the wiring harness at the components. You are trying to detect if there is any immediate or noticeable change. This is just a quick way to perhaps point you in the direction of a faulty sensor/ valve.

[Mike Sawyer]

I would look into whether your alternator is sufficiently putting out enough power to run all of the necessary components in your car. (headlights flickering) With the added amps for your stereo, you are really beating your Alternator to death; and if it is already weak…well you could end up stranded somewhere.

Good luck with this..

Doc

[Kulwinder]

Is there any way to check alternator ?

[Mike Sawyer]

I didn’t mean to infer that your amps/stereo was the cause of all of your issues. It would be a contributing factor with the flickering of headlights and such. A bad Alternator can wreck a battery, and a bad battery can cause premature alternator failure….add in a high powered stereo system and it is the straw that breaks the elephant’s back. Check for good grounds, clean connections. It is a good place to start. Drive without the stereo turned on…see if some of your issues go away…just an idea.

[Mike Sawyer]

Places like Auto-Zone and Advance Auto will do an Electrical check for free…

[Author]

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