carlyn

Hey all,
I have a (recently purchased) 1987 4Runner. Engine was rebuilt by previous owner ~20,000 miles ago.

On a cold start (in the morning, or after sitting 7-8 hours) the idle is very low/rough - if I don't give it gas it'll stall out. With a little gas I can shift into 1st and then it's good to go for the rest of the day. EXCEPT, once the engine is warm, it has a high idle in neutral ~1000 RPM +/- 50. I also occasionally notice an unpleasant gas/burning odor (though this may be unrelated/my imagination). MPG don't seem to be affected - at about 21/23 at the moment.

From reading other similar threads, it sounds like these are the things to check:
cold start injector/timer
clean injectors
clogged air/fuel filters
timing
cap/rotor wires
vacuum leaks
PCV valve

Is there anything else I should be looking at? Also, any advice you guys could give on prioritizing these possible problems would be awesome (i.e. what's the most likely cause and/or what's easiest to check/fix). I'm kind of (read:completely) new to the DIY auto repair game so I'm not really sure where to start! I do have Haynes, Chilton, and FSM manuals though so I'm not totally lost.

Thanks a bunch!

Stu Pidasso

It could be that your EGR is not functioning correctly. You can disconnect and plug one of the vacuum lines to it and that will disable it. If that were to fix it then I suppose you would need to look in to repairing that. Unless you have no emissions where you live or your truck is exempt. I need to look and see which one of the vac' lines you pull.

sechott

I fixed a similar problem on my 3 vze by cleaning the intake routing and adjusting the throttle and the air bypass idle settings back to spec. I think the previous owner adjusted the throttle to air bypass to help the symptoms.

ChefYota4x4

iTrader: (5)

Hey PO, welcome to 'GREMLIN FARMVILLE'! lol.....

Add to that list the testing of your IACV, it's very common for them to be stuck slightly open and not give you enough 'idle up when cold'.... But not likely to cause the rough idle stuff... That list you have is a good place to start....

.... But add "Coolant Temp Sensor" to that list as well. Also one that can take a dump on us. TPS isn't hard to test for problems as well....

As mentioned, cleaning out the throttle body(do NOT SOAK IT and get the TPS all filled up with Solvent ) doesn't hurt. Even cleaning the TINY ports to the EGR and other passages in the t-body can help.

Testing for the IACV is simple. But usually they just go bad. Is yours idling up in the morning at all after that lil hiccup stops?(Does it stop right away when you feather/take off? If so, when you pull over right away, is your idle at 'above' 750rpm where it's supposed to be? )

Best wishes on the hunt... you'll find it, sounds like one of your list or what I've added to me.

WJWoody

I am having the same problem and I figured out its the EGR Valve. And more specifically the EGR Temperature Sensor. The problem I am having is that I had the motor installed from a 1987 4runner to a 1984 pickup. The wiring harness doesnt have a hookup for the temp sensor, the mechanics(plural, cause I have had 3 try to figure it out) changed the wiring harness at least once possibly twice. Now, the wiring harness that is in doesnt have a hookup for the sensor.

Any Ideas on what I should do? Its idles somewhat ok and accelerates at startup just fine, but after 3-5 minutes it bogs down upon acceleration and is lacking power. My assumption is that it is running lean due to the Temp Sensor not being hooked up. $1600 and 1.5 years later its running better than it has, but this issue is not going away.

carlyn

Hey All,
Thanks for the advice! Just started school again :/ so haven't made much progress on the list, but did check for vacuum leaks (none) and changed air and fuel filters.
Tomorrow I'll adjust the valves and seafoam it - don't really expect this to solve the problem, but i think the truck could use it anyways and it's pretty easy !

RE:EGR valve - I just passed emissions so I don't have to worry about that for another year - will disconnecting it completely have any negative effects on anything besides emissions? (aka, is it worth spending $150 to get a new one?)

@ChefYota - Once I get going the idle stays low (600-750) for a little while (10 mins), then creeps up to 1000 as the engine warms up.

abecedarian

Why is it that everyone forgets... idle speed and timing... and even valve clearances... are set with the engine warm, at normal operating temperature?
When it's running right warmed up, it's easier to isolate things from the cold start side.

To begin with, the high idle with warm starts suggests the IAV under the throttle body is stuck.

People who tune things so it starts good when cold are compensating for things that are wrong and this affects hot starts and such.

ChefYota4x4

iTrader: (5)

ABE, Curious; What's more common with CTSensor issues... Chunky or HIGH idle in spots where it should already read "It's warmed up, stop it with the more fuel thingy!"? hahaha.... I KNOW what you mean on the IACV.... And to avoid trying a third one that seeeeeeeeemed fine, used, ... swapped in a new one and enjoy the idle up and then sloping down to 750 in a reasonable time that it provides! Lil pricey, but they just seem to wear out that arm/spring... And even replacing the spring with a good one, I couldn't get it to idle back down properly.

YEP on setting the valves warm.... They can give you tingly fingers for a bit, ...but WELL worth it, as things CHANGE, DRAMATICALLY, under different temps... They don't all change equally, either. YOU CAN do 'rough guess' stuff by adjusting for it being a 'cold valve adjustment, like .009 and .013... But it's just not accurate/proper way to get them 'JUST RIGHT' in the 'Happy Sewing Machine' realm.