Rough idle

[Steve Cornwell]

Rough idle – just put in new heads, head gaskets, intake manifold gaskets, New OEM upgrade fuel injectors, upper and lower Plenum gaskets, valve cover gaskets, ECT ECT ECT… still have rough idle – is most prominent when engine is fully warmed up, and is even more prominent after freeway operation WTF???!!! Any help in solving this issue would be greatly appreciated!
Thanks UAVMAN

Topic

[Jeffrey L DeBarto]

What make and model, year vehicle ?

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[Steve Cornwell]

It is a 98 Chevy Tahoe 5.7 L 4 x 4 , all repairs listed were completed within the last two weeks, I suspect a possible clogged catalytic converter or possible fuel pump issues, or unlikely but possible vacuum leak.

[Mike]

All plug wires connected to right plugs (happens to the best of us at times)
Any computer codes?
Compression was checked?
What are the fuel trims?

Hook up a vacuum gauge and see what vacuum readings are–they can tell you a great deal about what’s going on–including whether or not the cat is clogged.
http://www.gregsengine.com/using-a-vacuum-gauge.html
.

[Steve Cornwell]

Yep plug wires properly connected .. check
No computer codes or check engine light… check
Compression checks out good… check
Fuel trims… Need to be checked… oops, no check
Going to need to pick up a good vacuum gauge,… Any recommendations on gauges? … Types or name brands?
BTW thank you for the link on vacuum testing, it should prove very helpful as I advance from smog inspector to smog repair tech.

[Mike]

You’re welcome.
I’d get a fuel pressure tester, too, to quickly eliminate–or confirm– fuel pressure issues.
Sears used to sell decent/affordable test equipment but I don’t know about now.
Actron is OK and inexpensive.
OTC seems to be better made (they have a rubber cover to help prevent glass damage/breakage and they’re moderately priced.
Amazon has a vacuum tester that comes in its own case, which is handy.
The OTC fuel pressure tester is the one I use.

Am I right in guessing you cleaned the throttle body, IAC and the MAF sensor?
If not, that would be a good investment of time and little money.
Just don’t cheap out and use non-MAF specific cleaner on the MAF.
CRC brand is widely available, works well and fairly expensive.

[Steve Cornwell]

Throttlebody IAC and MAF were all thoroughly cleaned, although now that you mention it I’m wondering if I should do a little checking on the operation of the MAF.
As to your recommendations I definitely have to say thank you … A fuel pressure tester too huh? … Cool!
Looks like I’ve got some new toys to buy!!!
I definitely want to thank you for all your very useful input which I will be making great use of both now and in the future. Hopefully I will have the opportunity to talk to you again soon and perhaps talk a little shop.
Thanks once again
UAVMAN

[Mike]

Sure thing.
Look here for an article about one possible cause of rough idle on 5.7 and a number of other good articles
http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/rough-idle-after-installing-spider-injector-1

[Steve Cornwell]

I glanced over the first page and it was full of a lot of very useful information which I will be sure to use not only on my own vehicles but on any customer vehicles that I may repair it in the near future as I progress in my new profession … you’re not just out collecting thank you’s are you?! LOL
Once again thank you very much for all your great help and I will talk to you again soon, have a great day!

[Mike]

[quote=”UAVMAN” post=184947]I glanced over the first page and it was full of a lot of very useful information which I will be sure to use not only on my own vehicles but on any customer vehicles that I may repair it in the near future as I progress in my new profession … you’re not just out collecting thank you’s are you?! LOL
Once again thank you very much for all your great help and I will talk to you again soon, have a great day![/quote]

No but that idea did give me a good laugh.
In my never ending quest for more knowledge, I sometimes stumble upon helpful info and share it once in a while.
No one has all the answers and a quick glance at Mitchell, IATN, etc. lets you know that even seasoned pros need help every now and again.
You have a great day,too.

[Author]

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