2001 Silverado: Intermittent rough idle

Yankee00 · 10-03-2006, 11:31 AM

Where to start....first, I am new to these forums, but have found a wealth of information and appreciate everyone posting. Secondly, many of you sound very mechaincally inclined and I need to let you know up front that I did not receive the "mechanic gene" from my father

. I have a 2001 Silverado Z71, 5.3L with 128,000 miles on her. Now, on to my problem....

Initially, my "check engine light" came on about 4 months ago. My local mechanic stated that the error code meant that my catalytic converter(s) there are three on this truck, were going bad, but recommended simply resetting it since this was the first time. About a month later, same light, same error code and they convinced me I needed to replace the catalytic converter assembly

.

Less than a week later, I got in my truck and she would attempt to idle around 200-300 RPM, then die. Normal idle for my truck is 500-600 RPM. I managed to get her running and got it back to my local mechanic, but by the time I got there, she was idling normal. And she was fine for about a week, and then the same thing happened. I took it back to my local mechanic and although the problem was still occurring in their parking lot, there were NO error codes in the computer. They tried to get some TSBs on my truck to no avail and threw their hands up and recommended I take it to the dealer. The dealer could not duplicate the problem, so recommended I replace the fuel pump based on the mileage, so I did

. A week later, she acted up again. This time the dealer checked my throttle body and found it caked with carbon and they cleaned it. When I picked her up this time, she ran VERY

smooth and I sincerely thought they had found my problem as I read a few posts on this board with symptoms similar to mine and cleaning the TB fixed it. Well....the rough idle and dying is back. I have NO clue

what to tell my dealership to try next?

My concern lies in the fact that these symptoms were not present BEFORE the catalytic converter assembly was replaced. Do any of you have any ideas? Thanks in advance!

silverado122775 · 10-03-2006, 01:38 PM

Welcome to the Forums.

Do you know what the codes are? Before replacing Cats, I would attempt to replace the O2 sensor(s) first. But of course that would depend on what codes are being spit out.

3 Cats? I know there are 2 on mine. 3 would not make sense unless that was something added in 01.

Yankee00 · 10-03-2006, 01:43 PM

I do not know what the actual codes were when they told me I needed to replace the catalytic converter assembly. I questioned them about the 3 cats and it was explained to me that on my particular truck the assemby is in the shape of a Y, in that there is one type of cat in the neck, and two different types of cats in each leg?

Also, according to my mechanic, he was SUPPOSED to be replacing (and charged me for) 4 oxygen sensors. Apparently, their manual states to do this when replacing the cat. Hence my concern that perhaps some "step" may not have been followed when they replaced my cat and that is why my engine is now having issues? Not being a mechanic, I can only make guesses, though.

silverado122775 · 10-03-2006, 01:53 PM

Was this the Dealer that told you that or the Garage you took it? you can look under the truck and count how many you have. Cats are not built inside the piping. I think the guy is trying to rip you off. Here is what a cat looks like.
http://www.partsamerica.com/ProductD...pe=145&ptset=A

I know that aftermarket O2 sensors are about $80 a sensor. OEM from the dealer are about $100.
Aftermarket cats are about $80 each as well.

Yankee00 · 10-03-2006, 02:04 PM

This "mechanic" was from my local Firestone Service Center. All I know is that they charged me $900.00+ for the catalytic converter assemby.

silverado122775 · 10-03-2006, 02:08 PM

That would be about right if they charged you $300 dollars in labor.

Yankee00 · 10-03-2006, 02:11 PM

OK....I just went and looked. It appears to be just two actual cats, although the assemby itself is in the shape of a Y. I THINK I can see the 4 O2 sensors as well if there is one in fornt of and one after each cat?

TexasF355F1 · 10-03-2006, 07:32 PM

It's a strong possibility it could be your fuel pressure regulator.

Yankee00 · 10-03-2006, 09:08 PM

A buddy of mine recommended that I replace my key. He says there is a security chip in the key that could be going bad and causing this as he thinks the security chip directly controls the fuel pump. Any thoughts?

Yankee00 · 10-03-2006, 09:10 PM

What makes you think that Texas? And how would I be able to tell?

silverado122775 · 10-04-2006, 08:41 AM

Quote:

Originally Posted by Yankee00

OK....I just went and looked. It appears to be just two actual cats, although the assemby itself is in the shape of a Y. I THINK I can see the 4 O2 sensors as well if there is one in fornt of and one after each cat?

What you state is correct. one before each cat and one after each cat.

I beleive the first syptoms you would see if the fuel reguator went out would be difficult warm starts. But it is something to look into. The part is about $100 at a dealer.. I would not go aftermarket on that as you will see poorer gas millage. happened to me went from 19 hwy down to 12 hwy. after I put the dealer part in.. it went back up.

masapell · 10-04-2006, 08:54 AM

Quote:

Originally Posted by Yankee00

A buddy of mine recommended that I replace my key. He says there is a security chip in the key that could be going bad and causing this as he thinks the security chip directly controls the fuel pump. Any thoughts?

Hmmm? As a rule of thumb, I usually start out with the easier possibilities first. When your throttle body was cleaned, did they check the Idle Air Control valve on the side of the throttle body? It seems that if the TB was caked with carbon deposits that the IAC could be intermittently sticking, causing your idle issues. Anyway, it is something else to check into. One thing at a time.

Sincerely,
Matt

silverado122775 · 10-04-2006, 09:00 AM

That is a very good point!

Yankee00 · 10-04-2006, 09:00 AM

Matt,

I recall reading about the IAC in other posts where people had symptoms similar to mine. The dealership made no mention of checking this, simply that they cleaned my TB. Is this something a non-mechanic like myself could check, test or replace myself?

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