At my wits end with this 3.4... HELP.

M

Mudtallica

New member
I'll start with this... It's a 99 SR5, 3.4V6, auto... I'm having issues with the way it's running.. At idle, you can hear the motor revving up & down.. Put it in gear and it does the same thing when you give it gas.. Kinda like if you were pumping the gas pedal up & down a little bit but the RPM's do not fluctuate with the "sound" of the motor.. The check engine light is no longer on since I have changed out the following: Both O2's, both cat converters, muffler, plugs (Bosch), plug wires (NGK), all 3 coil packs (OEM), air filter (FRAM).. I took out the MAF sensor and cleaned it since it's only a yr old.. It's running better than it was but not perfect.. It didn't do what it's doing now before I changed all this... I can't remember the codes that it was giving me but I plugged up my scanner to check the I/M monitors and all was OK except the catalyst monitor and the EVAP monitor.. They were both "inconclusive".. Any ideas or thoughts out there would be greatly appreciated.. I do not want to take this to a dealership to have them "fix" this.. unless I HAVE TO..
 
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If your plugs are Bosch Platinum, get rid of them and replace it with some NGK/Denso Dual ground plugs.
 
x3, the intake air control valve uses a magnet that often goes bad. My friend helped me and changed the magnet with that from an old IAC from a 2nd gen and it works to this day.
 
The plugs could cause issues, but not so much as a crappy idle. It would be more along the lines of power issues and/or misfiring... something that would read on your OBD. I'll vote IAC.. If not, you've got yourself a vacuum leak.
 
It's not so much a "crappy idle".. I've done the A/C & lights thing.. No difference.. It's kinda hard to describe but here goes.. About a minute after starting it up, you can hear the motor fluctuate or pulsate so to speak.. Up, down, up down,.. As if you were lightly pushing the gas pedal down and letting off in a consistent rhythm.. This happens as it sits in idle & when you take off.. It's harder to hear or feel once you get up to 45-55mph but at 60 you can feel it sputter just enough to make you wonder if you really just felt that.. Waiting for it to cool off now to change out the plugs.. We'll see..
 
Make shure you check all your vacum lines as well make shure you didnt pull one out when you was working on it. But it realy sounds like a IAC to me there like 200$ new so I hope you can find a good used one or some thing.
 
A good way to test the IAC when it's idling is to take a hammer or mallet and give the throttle body a few taps. If the idle doesn't even out, i'd consider your throttle position sensor as those go bad, too.
 
Well, I took the TB off and cleaned it, took the IAC off & cleaned it.. Jumpered 12V to it to check it.. Works fine... Checked the resistance on the TPS, a little lower than what the manual calls for but close.. I'll get another one just in case.. The CEL is not on, so, to me, it's starting to seem like it may be a vacuum issue but I can't find any hoses that look bad.. Checked the EGR, idled like it's supposed to.. Timing is good.. Tried the "small hammer" to the TB & I'm afraid I'm might put it back & grab the sledge hammer!! Gonna change the fuel filter today and "try" to replace all vac hoses.. If there's any other idea's out there, throw 'em my way.. Thanks for all the "idea's" so far.. Eventually we'll get it..
 
Changed TPS, no change.. Replaced all vac lines from char canister to motor, same thing.. Waiting for it to cool off so I can get to the lines going to EGR.. Changed fuel fltr, tank was empty, so I poured in a bottle of Lucas FI cleaner & filled up.. Could this possibly be an injector issue? It runs, just not perfect & the wife doesn't like it.. Once again, my CEL is not on... Probably the first time I wished it WOULD come on..
 
Scan the codes anyway and see if there is anything stored in the computer

Spray some carb and choke cleaner around the engine bay and see if the idle changes. If it does, you have a vacuum leak somewhere
 
Scanned it, no codes... Went thru a new can of carb cleaner & nothing changed.. What I did notice was that it doesn't "purge" until it has warmed up.. Would the Temp Control Sensor cause this?..
 
Do you have access to a scan tool that you can read live data? If yes, check out a few different things. First, when warm, is it entering closed loop mode? Watch the temp reading. is it fluctuating? also, what are the o2 sensors doing? Sensor one should bounce around and sensor two readings should stay fairly flat, as long as your catalytic convertor is ok. What does the short term and long term fuel trims look like? Those will be shown in percentages. Positive percentages mean that it is running lean and the computer is dumping fuel to compensate. Negative percentages, engine running rich, pulling fuel to compensate. Short term is what it is currently doing, long term is over a given time period. Lastly, get the specs for what the mass air sensor should be reading at idle and at 2500 RPM. if they don't match, the MAF sensor may be bad. Hope that helps a bit.
 
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Thanks man.. I'm tryin' to get my hands on a scanner that will show live data.. Mine does not.. I had to take a "mental" break from this thing..!! It runs ALOT better since I've changed all that I have & has great throttle response but it's this "purging/surging/fluctuating" thing that's driving me crazy.. As soon as I can get my hands on this Blue Point Microscan tool, I'll air out all it tells me... One question though.. If the O2's, or MAF sensor were "bad", wouldn't it give me a CEL? Or can they go "kinda" bad.. You know, just enough to screw with ya without lightin' up your dash? Just curious.. By the way, the CEL is still not on.. Thanks again for all the ideas & suggestions.. I am catching myself spending way to much time on here.. It's bringing out the "reader" in me..
 
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