Hesitation and clunk during start

[Yugo]

Hello, I have a 2007 tahoe w 135k miles. Have recently change plugs, wires, fuel pump, no cell or any other issues. Maf is also clean.

Every now and then when I try to start the truck, it cranks, but rpms drop and it hesitates for a second or two before it brings the rpms up like on a normal start. It's also accompanied by a clunk that seems like it comes from bottom left side (drivers side) of the engine.

I have researched all over the net and can't find anything conclusive. I am hoping that someone on here has an answer to it. Thanks

 

[AZSCTACO]

Has the throttle body been cleaned ever? Clunk might be a motor mount??

 

[Yugo]

Has the throttle body been cleaned ever? Clunk might be a motor mount??

Haven't cleaned it since I have owned the vehicle and I highly doubt it was done before. Plan is to clean it this week and hope that will help the issue.

This starting issue developed about 2 months ago, right after I ran a few ounces of seafoam thru my oil for about 200 miles as suggested. Not sure if just a coincidence.

 

[AZSCTACO]

Might want to get your injectors professionally cleaned.

 

[Yugo]

Might want to get your injectors professionally cleaned.

Good idea. Have been running techron cleaner approx every 1k miles. But still occasionally get the slight vibration in the steering wheel when idling. Don't notice rpms jump.

My biggest concern is that my starting issue isn't related to something serious or something that can leave me on the side of the road especially since I am planning several family trips this year.

I have replaced so many things on this truck lately that I am getting to the point of letting it go and going the minivan route, since newer tahoe/Yukon isn't in the budget.

 

[Yugo]

Update - I have noticed the hesitation only occurs after I start the engine immediately after the key has been inserted into ignition.

If I wait a few seconds after inserting the key into the ignition, turn it to on position, but don't crank it yet, and after it has stopped "beeping" I turn the key, it starts just fine. No issues.

What could that mean?

 

[AZSCTACO]

I'd say take a look at the fuel pump....even though you changed it. Have a mechanic hook up a fuel pressure gauge and see if the pressure drops. Might be the fuel pressure regulator issue. I believe they are build into the fuel pump.....maybe someone can clarify. Sounds like it starts fine after the pump has time to prime after your key is turned to the on position. Keep us posted.

 

[Yugo]

Update - took the Tahoe on a 1,600 mile trip 3 weeks ago. During the trip noticed that my mileage is about 17.5mpg which I questioned, since last time I took it on a long trip I avg. about 20mpg with similar amount of luggage as before. 2 days after I got back from my trip I get a CEL for a bad pre-cat O2 sensor. In order to prevent any more damage to the cats, I immediately ordered and replaced both pre-cat O2 sensors. Haven't noticed the weird "clunk and starting hesitation" issue anymore. Hope it treats me as well on my 1000+ miles trip next month. Thanks again for all the input here!

 

[AZSCTACO]

Thanks for posting an update.........