1fz-fe randomly idling rough and gutless

[A1aardvark]

Hiya
Just got my 8o 4.5 auto out for first real run on Sunday since I purchased it a month ago. 6 hour drive with about 2.5 hours in low range and it didn't miss a beat. I took it down the shops Tuesday and alls still good but Wednesday morning I went to move it a few meters and it started idling extremely rough and nearly dying. Contacted previous owner and he admitted that it had done this before and had his mechanic go searching. His mechanic couldn't find a cause but cleared up on its own so he stopped worrying about it. Drove it today trying to find a pattern and but it seems very random.


Here's the symptoms


Starts fine but idle gets rougher and rougher and in about a minute it nearly stalls


Rev it a bit and it may just about go back to normal or may not


Doesn't matter if it's hot or cold


When it's doing it the car drives sluggishly in lower and middle rev range but seems fine in upper revs


May clear up for a while randomly


Also I havent done any water crossings since I purchased but have been down a few bumpy roads. Previous owner never did dirt.


So far I've checked the condition of tubes and intake for vacuum leaks. Also tugged and pushed on wires and vacuum tubes randomly while the engine was running. I also had the the compression of the cylinders check when I bought it and and it was even across all six.


I've done lots of googling and problem is people seem to described similar problems very deferentially. So far it seems the candidates are vacuum leaks, O2 sensor, MAF sensor, sensor wiring/plugs and coil/leads. Also read one post about fouled exhaust valves giving similar symptoms.


Given the random nature of the problem does it seem like any of these are most likely???

 

[clivehorridge]

Random sounds like HT going to ground, when it shouldn't.

I don't know the 1fz-fe so I can't help on the more technical stuff that's likely to fail...

Not much help but...

 

[A1aardvark]

Random sounds like HT going to ground, when it shouldn't.

I don't know the 1fz-fe so I can't help on the more technical stuff that's likely to fail...

Not much help but...

sorry whats "HT" ???

 

[clivehorridge]

sorry whats "HT" ???

"...sensor wiring/plugs and coil/leads..." the red ones from your list would qualify.

High Tension or the spark wire from the coil to the distributor and out to each spark plug. The High Voltage can jump to ground almost anywhere along the run, especially if it's damp weather or if the leads are old...

 

[Gary820]

Ht leads are the leads to the spark plugs.


Basics first, when were the spark plugs last changed? The part of the ht lead that goes down onto the spark plugs, in good condition? I had a misfire caused by one of those bits failing.
Condition of the Distributor cap and rotor arm.
Fuel filter, air filter, again when were they done?

If the oz spec 1fzfe has them the egr valve ( exhaust gas recirculation valve) could be stuck open, blocked exhaust/ cat converter.

 

[A1aardvark]

Ht leads are the leads to the spark plugs.


Basics first, when were the spark plugs last changed? The part of the ht lead that goes down onto the spark plugs, in good condition? I had a misfire caused by one of those bits failing.
Condition of the Distributor cap and rotor arm.
Fuel filter, air filter, again when were they done?

If the oz spec 1fzfe has them the egr valve ( exhaust gas recirculation valve) could be stuck open, blocked exhaust/ cat converter.

no catalytic converter on my model but does have egr.

last night I ran it in the dark to look for arcing but no luck. Ironically after about 15 minutes the engine note changed and it ran normally for a short drive but I it's not hot and cold thing cause it happens anytime.

the night before it started happening I did drive a short distance in heavy rain so I do think its electrical. Yet to start it today.

 

[Gary820]

A good trick to give the ht a leads a wet test, get a spray bottle with some water in and spray a mist of water round the leads. If one is breaking down it'll arc quite well. It will rule out the ht system rather quickly too.

As I posted above, I had a lead fail where it goes down to the spark plug,

After that check the egr, air leaks. I think the air intake pipe after the maf are good for splitting?

Not sure if the same for these, some vehicles when the maf is un plugged they go into a default mode, if so it's a quick way to rule the maf out.

Not many of us with petrol over here and very few faults afaik

 

[Rich Sims]

Could be a blocked fuel filter?

 

[Richard Jackaman]

Or a blocked fuel filler breather? Is the filler difficult to get off and does it hiss? Try running with the filler cap loose if it happens again.

 

[A1aardvark]

Maybe got to the bottom of the problem.

There's a t off the booster vacuume hose for an aftermarket cruise control. Found last section to cruise control was perished so put in a new bit. This slowed down the transition to poor idling but didn't stop it. The t has no hose clamps on the booster pipe so I'm thinking it's still leaking slowly. Probably explains why it runnings ok at max revs cause more vacuum might be over coming the small leak. Also if when I had the small pipe off it created exactly the poor running symptoms I've been experiencing.

What's getting me is why the mechanic who went looking for the problem didn't just chuck on a vacuume gauge? Also the perished pipe was really obvious.

 

[Gary820]

Or a blocked fuel filler breather? Is the filler difficult to get off and does it hiss? Try running with the filler cap loose if it happens again.

Good call

 

[A1aardvark]

Good call

well it's worth a try ...

 

[Shayne]

It might seem too easy but i have found this stuff can bring about astonishing improvements i stuck it in a 15 year old ford transit tipper my crew use which despite being mechanically sound had no go in it whatsoever , i was asked by its usual driver afterwards what i had done to it .

 

[Gary820]

Would use a petrol version though ;-)