strange problem w/ idle

[aleahey]

my 5.0 has developed some sort of hiccup all of a sudden. it runs very rough at idle, like its constantly searching for it. i cleaned the egr and throttle body, as well as the little other thing that i cant seem to remember's name. i recently put a new fuel pump in it, new fuel filter, and this problem didnt seem to improve.

when i hit the gas, the idle actually decreases for a second, and then surges. it also seemingly delays when i remove my foot from the gas. if i press the accellerator too quickly while in park, the car will actually stall.

another note is also all the lights in the car seem to get brighter/dimmer as i press the gas and release it. realize thats probably an alternator problem, or perhaps caused by having a low idle. im hoping its the latter, and someone has some advice. thanks.

 

[aleahey]

just a note, i did read the sticky, but i dont believe my problem fits the surging idle checklist. if you think it does, and i should just follow the instructions within....woops

 

[bcd]

un plug the iac motor and see if it stops. mine was doing all kinds of crazy stuff due to a bad iac

 

[aleahey]

trying that right now, ill hitcha back in a few.

thanks for the reply too

 

[aleahey]

no go, its worse if possible. now it doesnt even want to start/stay started. it acts like the idle is way too low but when i checked the idle control screw its actually screwed in about as far as it will go.

 

[bcd]

if it wont idle with the iac unplugged then the idle is set wrong. from what i have been told

 

[HISSIN50]

The unplugging of the IAC is only a valid test if one follows the MM method of idle setting and does it on a HOT motor. The IAC is needed for a cold motor to idle decently.

WHat is the cold and warm idle reading now?

Are there any codes stored? Codes can be stored without a CEL being on.

Good luck.

 

[aleahey]

code 34 :\

 

[HISSIN50]

34 is an EGR code. I would address that first. Though I cant recall the verbage on that particular code, if you have EGR being introduced at idle (when it should not be), it will make the car idle like poo and stumble.

Jrichker has a very nice write up on code 34 and what to do to diagnose it. I would search his posts for it and check out that code further. I would do this before adjusting anything with the idle, if this issue just popped up out of the blue. No need for extra variables to be introduced.

Good luck.

 

[aleahey]

well i took apart the egr valve and cleaned all the carbon out, figuring it was probably stuck open. inspected it for holding a vacuum, and it seems to function fine. i attached a vacuum gauge to the vac line that goes in to the egr valve and it didnt ****e, or rise at all, so there doesnt seem to be a call for the egr at idle as you suggested. im seriously stumped. at this point, now, the damn thing wont even turn over. it comes remotely closer to turning over with that IAC unplugged, but not much.

yet and still, code 34 :\

 

[HISSIN50]

at this point, now, the damn thing wont even turn over. it comes remotely closer to turning over with that IAC unplugged, but not much.

yet and still, code 34 :\

It truly wont turn over, or it wont catch. Sounds like it turns over but wont catch. Otherwise, charge the battery up if it wont turn over.

Good luck.

 

[aleahey]

sorry, wont catch. i actually did charge the battery as the lights were dimming quite a bit but that didnt help any.

 

[aleahey]

any idears?

 

[jrichker]

Code 34 Or 334 - EGR voltage above closed limit - Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with carbon remover. Prior to re-installing see if you can blow air through the flange side of the EGR by mouth. If it leaks, there is carbon stuck on the pintle valve seat, replace the EGR valve ($85-$95).

If the blow by test passes, and you have replaced the sensor, then you have electrical ground problems. Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery post. It should be less than 1 ohm.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other. Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending on the sensor. The center connection of the variable resistor is the slider that moves in response to the amount of vacuum applied. The slider has some minimum value of resistance greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish between a properly functioning sensor and one that had a broken wire or bad connection. The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at rest with no vacuum applied. The EGR valve or sensor may cause the voltage to be above closed limits due to the manufacturing tolerances that cause the EGR sensor to rest at a higher position than it should.

This will affect idle quality by diluting the intake air charge

 

[aleahey]

okay, thank you all, i seem to have solved my idle problem. HOWEVER there is now a new problem. it idles fine but when i press the gas, it hesitates and acts like its going to stall and a moment later it revs. sound like injectors or wha?

thanks.

 

[Paul Perreca]

get new EGR - if its messed up, just get a new one