dr1553

I have searched and read threads on rough idle and bad timing and still havent figured this out.

My truck has a rough and low idle when warmed up.

When I first start it up it goes to 1,100 then drops down to 800 after a few minutes. It only idles low when its warmed up after driving for a few miles, then when I get to a stop light it drops to 3-400rpm. This is with the clutch in and the a/c, fan off. It is also hard to start when hot because it wants to run at 400rpm. I have to hold the gas pedal in a little to get it to start warm.

With a timing light and jumper wire in (timing changes very little with wire in) the timing jumps between 8 and 11 deg and every couple of seconds it will jump up to about 15. This is when its idling at 800.

I dont think its the idle speed that needs adjusting because most of the time it idles at 800, just sometimes when it hot it idles down low. But it always idles rough. Idle adjustment screw does nothing anyways so I put it back where it was.

The truck runs fine when I'm driving, its only rough at idle.

No codes are showing or stored.

I put in a new timing belt last year.

IT has new plugs, cheap NGK like everyone on here says to use.

I have tried two sets of cap and rotor, and OE and an Oreilly set.

New fuel filter, helped with starting, was hard to start always, now only hard to start when warm.

I have hooked up and ohm meter to the TPS and I do get a change when the throttle is just begining to move. I dont get a change at WOT, not sure if I should. I havent tried to set it with feeler gauges yet because I dont have a gasket so I havent pulled it off the intake yet. I guess this is my next step.

The intake is clean, I had it off when I did the valve cover gaskets last summer.

I have ran seafoam thru it.

I dont think the EGR valve does anything because the EGR valve modulator is all busted up. Also the tube from the EGR to the intake doesnt get hot so I dont think gas is flowing thru it.

Has a good OE thermostat in it.

I have looked for vacuum leaks with propane and a can of intake cleaner, no change in idle, I sprayed all over that thing.

It almost didnt pass inspection a few months back becasue of low speed noX, it only passed by 1ppm. High speed noX was fine.

Ok, I hope I have given enough info to go on. Does anyone know what would cause a rough idle like this and why my timing jumps all over the place?

Sometimes I really wish it just had a carburator.

Thanks!

dr1553

I found and old post by Elvota that said he had timing problems and he changed the distributor and that fixed it. I guess I'll try that. I did notice oil under the cap, so I guess I'll try cleaning it out first. I guess oil is traveling up the shaft of the distributor? Does anyone know if there is an inner o-ring or some kind of seal that is supposed to keep oil from getting up there?

I'll post if I get it figured out.

Chief_Yota

DEFENETLY THE TPS DUDE!! stop looking around its your tps ,i had the same crap,i changed for a new tps (by the way its really an expensive peice)
bout 200bux,because i though mine was broken,but it wasnt,its just really really hard to adjust you have to go really slow and get it the more close you can to the manual spec, make sure its tight too.

dr1553

Your timing was jumping around? I dont know how the TPS would do that? The timing light picks up the signal between the distributor and the spark plug so to me it makes sense to be the distributor. How could the TPS make the timing be off? I thought the TPS monitors the position of the throttle (T.P.S.) and keeps the air/fuel ratio happy. Maybe the engine is running bad due to a bad TPS and the computer is trying to make it run better and so is changing the timing trying to fix it?

I will try both the TPS and the distributor.

thook

Try one thing at a time so you can keep better track of what's happening....what's working and what's not.

The TPS will definitely affect timing.
http://www.off-road.com/toyota/tech/tps/
You can start there first. It's much more common than a problem distributor, even though neither may be your problem. There are other things that will cause your problem. With EFI the water temp, air and fuel ratio, and timing are interrelated and one will affect the other via the lovely little component...the ECM. So, you are going in the right direction there.

When you go to test the TPS, don't loosen it yet as in to "set it". Use the feeler gauges to test the resistance values. If they don't read like they should, then it's bad. If it's good, then you haven't messed with the position of it.

thook

Hmmmm ....don't how this happened, but it did. Mod's please delete this double post.

Bigblock

Timing jumps around on most anything with a piss poor distibutor.Idle it up and forget it.Which idle screw were you refering to?You may need to remove the throttle body and clean/replace it.Also you need to check fuel pressure hot/cold and in between.And 30 minutes after you turn it off.In other words,put the guage on there and drive like normal until you're satisfied that f/p is ok.

dr1553

Ok....looks like the TPS is the next thing to try. I need to order the gasket, or I might try to use the old one. I need to get it off to test it properly. Not enough room to get the feeler gauges in there without removing it.

I was adjusting the screw on the side of the throttle body. The air bypass screw. It didnt make much difference.

My ohm meter has two resistance settings. RX1K and RX10. Which one do I use to check the TPS?

Also....if the TPS is bad, are the aftermarket ones ok? Napa, Oreilly and Autozone all carry them.

Any ideas why oil would be in the distributor?

Thanks for all the help so far everyone!

dr1553

Finally got to check the TPS. It checks out good. So its not the TPS. Idle still bad and timing still jumps around.

I guess I have to look at the distributor next. The fact that oil is under the cap pooled up in the distributor has me thinking thats my problem. I'm going to find a way to clean it out and see if it runs better.

shurup

Idle screw has no effect on idle speed when the engine is cold and is not enough to warm up the engine. Try adjusting the idle screw again after driving the truck around for a bit and if it makes no difference then you have some vacuum leaking problems I believe (I will check my sources and will tell you for sure).

TNRabbit

There IS an O-ring on the distributor shaft. Sounds like you've checked everything out but the distributor; does it have any play? Is it really coated with oil or just a little residue? Remove it with the crankshaft set to TDC and don't turn the engine over while it's out then be sure you put it back in the same way. Check to see if there's any obvious issues/wear inside.

BoostinChick

Did you figure out your problem? I have a very similar problem and have replaced or checked the same things.

Replaced:
VAFM
TPS
Coolant Temp Sensor
Spark Plugs
Spark Plug Wires
Cat
o2 Sensor
Fuel Filter

It was suggested to me to check the fuel pressure regulator and the cold start injector next. Just seeing if you figured your issue out since my symptoms are very similar. I may go the route of checking my timing first though before I get more in depth with the fuel.

1993YotaRunner

Any closure to this problem? My friends 1990 4runner is doing the exact same thing. We worked on it today and all possible fixes did nothing.

Just seeing if you found a solution.

dr1553

Sorry about no response. I had forgotten about this thread.

To answer the questions....NO. It's worse. It still wants to start at only a few hundred RPM's and now sometimes it runs WAY WAY slow for about 5 seconds and the check engine light comes on. Then the idle kicks up to 4-500RPM and the light goes off after a few more seconds. It only does this after it is warmed up, it never does it first thing in the morning but it does it when I goto lunch. It does ALWAYS idle rough however. I just had it inspected and the guy told me he was worried about it because it had a little miss in it at idle but when he gave it a little throttle is smoothed out. It passed the smog test fine. At idle the gear shifter vibrates around....when I first got the truck it didnt do that.

Also when I was on the way to get it inspected I wanted to give it a good run so I floored it away from a stop light and at 3500RPM it started cutting out bad! I never accelerate hard with it so I had no idea it would do that. It has a new fuel filter so I dont think that is the problem.

Now in the past few days I have noticed a very strong gasoline smell at startup. It goes away after about 15 seconds but its strong right at startup. I looked around under the hood and under the truck and couldnt find any gas anywhere.

I'm thinking maybe my injectors are goind bad? It has 180K on it.

If anyone has any ideas I'll try it. Something it wrong.

dr1553

The truck is still having the same problem. Since I drive it less than a thousand miles a year it has not been a priority. But it still bothers me.

So I took it to a guy that knows these older Yota's. He said my cat is clogged or broken up inside. He said that he has seen the insides break up and turn sideways clogging it up. That causes the engine to have a tough time breathing right....it cant exhaust properly.

He said he is 99% sure thats the problem, since he has seen the exact problem a few times before. He knew from the way it sounds and smells at idle.

So soon I will be pulling the cat, should be easy since it is flanged, and I will find out.

Has anyone else had a bad cat make your truck run so bad? I guess its an easy enough fix if that is the problem and it probably would not hurt to change it anyways. I will have to check and see if the junk yards are still paying big bucks for the old cats!

airkewld4life

I had a clogged cat, replaced it with a hi flow Magna Flow and noticed the problem go away.

dr1553

It had the same symptoms? The rough idle, smelly exhaust, sometimes a really low idle at startup, bucking under hard acceleration....ect?

Plus I have only been getting 8 MPG driving it very easy, very slow starts and all.

airkewld4life

All the above except the jumpy timing. Note, I also changed my o2 sensor. That helped out tremendously with gas mileage.

Kiroshu

I've yet to dig into it cause i have no time but i have a friend of mines 4runner with the exact same issue down to the tee. But the cat is gutted in so i know its not that. I think the trucks been messed with by the "PO" so i think the idle screw is turned in too much and a possible vac leak but not sure yet have not had a chance to mess with it but my friend tried everything you did lol. The one thing i know is right is the TPS cause i set it. I'm guessing the idle has been adjs and its all wrong. I plan to check the fuel pressure and look for vac leaks soon on it.

airkewld4life

If I'm not mistaken, a hollowed cat can still clog. Definitely check for vacuum leaks. I'd be willing to bet that you have one