Idle Issues

[Va_Disco]

So I have been having a strange idle issue for the last month. The symptom's are hit or miss and come and go on a whim.

On start up it will either idle high (1000-1200 rpm) or will idle low (300-400 rpm) and will slowly after a min of so come up to the normal range ( 700 rpm ) Unless of course it decides to idle properly from the start.

After it settles at normal idle and with it still in park if you tap the gas and bring the rpm's up the idle issue will return and after about 20 seconds will slowly return to normal rpm.

While driving and the truck preforms flawlessly, until you come to a stop and then it will repeat the idle issue similar to when you tap the gas in park.

The truck has 160,000 miles and just had a tune up (plugs, wires, oil) I has new O2 sensors. The MAF has been swapped to check if it made a difference ( it didn't) The Idle air controller has been swapped (didn't help either) The TPS is working properly based on the reading from the scanner.
I just replaced the injectors with the Volvo upgraded ones (The truck ran seamlessly for a few days after this, and now the problem is back. but as I said it comes and goes as it wishes)

The fuel pump was replaced about 4 years ago, But when I swapped the injectors and bled the fuel rail there wasn't much pressure. I am beginning to believe that the fuel pressure regulator is going bad. I haven't put a pressure gauge on it yet, probably will this evening and will report what I find.

I am just wondering if anyone else has had this problem? I am interested in any feed back to make sure I am addressing anything that could be the problem.

 

[Bannon88]

When was the last time the fuel filter was replaced?

 

[Va_Disco]

The fuel filter was replaced when the fuel pump was done (4 years). If it was a filter issue I would expect problems with accelerating and higher speeds because of a restricted flow from the filter. But it runs great with no hesitation doesn't matter if I am doing 25mph or 70 mph.

But It is a cheap part and I will probably replace it anyways.

 

[WaltNYC]

I've experienced similar idle issues after my battery has run down requiring a jump start. Clearly not conclusive, but worth checking.

 

[Va_Disco]

I have a new marine deep cycle battery in the truck. It did get a jump start recently but the problem existed before that. A standard battery could have a problem after being totally drained and having to be jumped. But Deep cycles are designed to preform in such a manor.

Was it just the battery dying that cause your issues? Or did the lack of power cause something else to become problematic?

 

[WaltNYC]

Was it just the battery dying that cause your issues?

yep.

But again, I wouldn't conclude anything, just something easy to check.

 

[Va_Disco]

WaltNYC

Okay, well I think I can rule that out for the moment because the issue was going on before the jump. But thank you for your input.

 

[drsus]

Funny, came here to post a thread on exactly this problem on my truck.

My idle is very erratic like yours. When it's cold it almost always acts perfectly. Starts high and strata to settle down to where it should be as it warms up. Once I start driving it it all stays the same. The issues start once I shut it off and restart it, that's when the bide decides to either be super high 1000-1200 or super low almost stalling (300-400). A lot of times its almost the same sequense... Cold start good, next start low idle next start high idle and then it tends to stay at high idle starts version of it. The only time it returns to normal is if I let the engine cool down significantly... Almost as if it was a fresh start.

I should mention the truck ran beautifully until I decided to park it for a long time, with battery disconnected so I could to all the mods to it from stock. The when I re hooked up the truck never ran good again, go figure. I've replaced the idle air control, only played with unplugging the tps to see if it would change things (nothing), replaced the temp sensor (the one to the the computer, not the thernmostat sensor). I'm stumped.

 

[Va_Disco]

Mine stopped showing any kind of problem as soon as I posted and it stayed fine until today where now it's doing the same thing again I'm beginning to wonder if it's a ground problem I'm going to pull all the grounds and clean them and see if it makes anything better

 

[drsus]

I'm replacing my O2s... it keeps failing the smog check because of o2 failures and land rover says they're to be replaced at 60k anyway so... I'm going for it regardless and somewhere in a little corner of my heart theres hope that this fixes things being that the O2 sensor is somewhat involved in idle control after many other factors....its thin but I'm out of guesses here.

dont look at the numbers when the shop hooks up the analyzer to it, it'll make your head explode... my truck thinks its going 1350mph while sitting still, it thinks its -60 degrees temp and then it thinks its 200 degrees.... this when its sitting there idling beautifully at 800 rpm.