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Startup Stumble When Warm

SteveCZ

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SteveCZ Enthusiast

SteveCZ

Posted
Posted

Well, last weekend I decided to give my K&N Drop in Filter a good cleaning, since its been over a year since I last did it.

 

After I rinsed it out and let it sit for about half an hour, I decided to spray down the Mass Airflow Sensor with some electrical cleaner (since this has been reccommended on here before).

 

 

I then proceeded to remove the intake boot and check out how carboned up my Throttle Body was... and it was filthy, and I had a sticky gas pedal too, so I was figuring it would be dirty.

 

I sprayed a little bit of Top Engine cleaner around the back side of the throttle plate, and it cleaned it up real good...

 

I put everything back together, and it was fine until yesterday after the truck was sitting outside for a while in the parking lot at work.

 

I fired it up, and it kind of stumbled first, then idled fine and ran fine.

 

This happens now (to a slightly lesser degree) every time the truck is warm, but sits for more than 10 minutes. Its fine on Cold Start in the morning (no CSK, by the way), or if I shut the truck off and within a few seconds, start it back up.

 

I don't know if I screwed up the MAS by hosing it off with Electrical cleaner or if the TB is messed up after cleaning?

 

SnoMan, any help?

carguru Senior Enthusiast

carguru

Posted
Posted

A couple of questions. Did you let the sensor dry off? Did it set the check engine light? When you reoiled the K&N, did you lightly oil it only? My thoughts are if it was oiled too heavily, some of the oils will be pulled through the filter and coat the MAS after you cleaned it. By cleaning the sensor, you should not have done any damage. Well as long as it is with a decent electrical contact cleaner or throttle body cleaner. Did you hose down the throttle position sensor with throttle body cleaner also? This is a possiblility that this is affecting the stumble/idle. Just a couple of thoughts.

SteveCZ Enthusiast

SteveCZ

Posted
  • Author
Posted

Thanx for the quick response.

 

Yes, I let the sensor dry fully after I cleaned it....

 

I did have a little excess oil drip off of the filter before I put it in.

 

But I made sure that it was pretty well soaked up before I put it back in the truck.

 

I cleaned the MAS again after work yesterday, and it seemed to help a little bit.

 

Should I try to spray some throttle body cleaner in the Pilot air hole for the idle circuit (the hole on the top of the Throttle body opening) to clean any leftover crud out?

 

Like I said, it idles PERFECT after the initial stumble, better than new, and only when its warm.....

snoman Senior Enthusiast

snoman

Posted
Posted
Thanx for the quick response.

 

Yes, I let the sensor dry fully after I cleaned it....

 

I did have a little excess oil drip off of the filter before I put it in.

 

But I made sure that it was pretty well soaked up before I put it back in the truck.

 

I cleaned the MAS again after work yesterday, and it seemed to help a little bit.

 

Should I try to spray some throttle body cleaner in the Pilot air hole for the idle circuit (the hole on the top of the Throttle body opening) to clean any leftover crud out?

 

Like I said, it idles PERFECT after the initial stumble, better than new, and only when its warm.....

I would not recommand cleaning the MAS with anything but air pressure or a light brushing. The cleaner you used is pretty powerfull and if may have altered the surface properties of it by minutely chemically etching it and leaving trace molecules on it as well. Cleaning it was the start of your problems and by using a oiled air filter, you have set yourself up more in my opinion. Oil does evaporate (though in very very small amounts) and is injected into the air stream that flows over the MAS sensor leaving oil molecules on it to collect dust and effect its operation. All though in theory a oiled filter is good in a dusty environment, I would never use one on a engine such as yours. There are a lot of good dry filters out there.

SteveCZ Enthusiast

SteveCZ

Posted
  • Author
Posted

Well, I think my truck found out that I was talking about it on here

 

:thumbs:

 

After I drove home after work, and it got warmed up, same as before, now its fine... so maybe there was just enough oil coming off of the K&N to screw up the MAF Sensor.... but cleared up after some air blew it off???

 

Its fine now either way...thank god... I didn't feel like replacing a MAF Sensor for 150 bucks due to me being stupid

 

Thanks for the responses

 

SteveCZ

carguru Senior Enthusiast

carguru

Posted
Posted

Hope that solved your problem. As long as you didn't spray the electrical cleaner on a hot sensor and allowed plenty of time for it to dry before using, it should be ok. Even a little oil getting on the sensor wire can cause problems. The same goes for cleaner residue. :thumbs:

  • 3 weeks later...
SteveCZ Enthusiast

SteveCZ

Posted
  • Author
Posted

Got my truck fixed yesterday by the dealer (thank god for the GMPP 5 yr / 60k)

 

Turns out it was the fuel pressure regulator.

 

Just kinda scared me that I did something because the truck started acting up as soon as I cleaned the TB and my K&N drop in filter....

 

So I now have a nice clean filter and MAF Sensor, and throttle body, and a new Fuel Pressure regulator.

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