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Causes of a Rough Warm Idle?

Old 05-08-2019, 08:46 AM
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Unhappy Causes of a Rough Warm Idle?

What are some items to check for with a rough warm idle? No check engine lights unfortunately. I am scratching my head on this one, I'm honestly to the point of having a professional mechanic to look at it which I'm sure will cost big $$ that I don't have. What are the chances of it being either:

1. O2 sensors
2. Leaking EGR
3. Vacuum leak that I can't find
4. Mass air flow meter
5. Engine coolant temp sensor

Truck idles high when cold but as it warms up, the idle gets rougher. Half the parts on this truck are brand new and its quickly siphoning out our wallets. Truck is an '89 pickup 22re with 113k on the odometer. I apologize for starting lots of threads, I'm just really desperate at this point!
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Old 05-08-2019, 01:28 PM
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It's frustrating sometimes to solve issues on these old trucks. You need to be systematic and go through things carefully and you'll figure it out.

The FSM for my 1988 4Runner under rough idle says:
Spark Plugs
Spark Plug Wires
Ign Coil
Igniter
Distributor
Incorrect timing
Vac leaks (PCV, EGR, intake, air intake chamber, throttle body, pulling in air between afm and throttle body i.e. the air intake hose)
Incorrect Idle speed
EFI System issues
Engine overheats
Low compression
Incorrect valve clearance

There are checks in the FSM for a lot of this stuff, if you don't have the FSM, you need it and it's easily found on the internet. The FSM troubleshooting doesn't really seem to make a distinction between a rough warm idle and a rough cold idle, but is your warm idle speed correct? Have your valves been adjusted? Has your timing been set? Age/condition of your spark plugs, wires, distr cap, rotor.

You need to stick to a single post and collect all the info in one place so that people who are trying to help you can easily see what you've already done, I didn't go look at your other threads and I really don't want to have to have several threads open to know what all is going on.
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Old 05-08-2019, 02:03 PM
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Tight valves???
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Old 05-08-2019, 03:02 PM
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X2, stick to one thread..

The first thing i do is a viisual inspection everything is plumbed correctly. Next set the idle and verify timing. Then pull the sparkplugs and look for signs that might indicate a particular cylinder, like a bad valve seal or damaged sparkplug for example. Followed up by cold, hot, and wet vs dry compression.


I don't recall that you've posted audio/video of exactly what it is doing either. "Rough idle" is kind of subjective.
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Old 05-09-2019, 08:24 AM
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Thanks for all the replies!

The truck has been sitting for almost 15 years and now that I'm getting my license soon, I will need it running so I can use it. Here's what I've replaced over the past year:

1. Spark plugs & wires (gapped to 0.32)
2. Distributor cap & rotor
3. Fuel pump, tank, filter, injectors, pressure regulator
4. PCV valve & grommet
5. TPS
6. Thoroughly cleaned throttle body and IAC valve (the coolant lines to the IAC valve are hot when the engine is up to operating temp)
7. Air filter
8. No cracks/ holes in intake duct
9. Throttle body and upper intake gasket
10. Coolant flush & thermostat (gauge only goes up 1/4 of the way at operating temp, is that ok?)
11. Cleaned EGR

The truck starts up cold and idles around maybe 2,100 RPM (no tach) which seems a bit high to me but still runs well. About a minute or two later, the idle drops and gets rough with occasional sputters so I have to have my foot on the gas to keep it from stalling. I've tried to mess with the timing but the closer I get it to the "5" mark, the engine wants to stall (TE1 and E1 are jumped with CEL flashing and idle still drops). The idle adjustment screw seems to have no effect either. Pumping the brakes rapidly also makes the truck sputter.

We drove it around the neighborhood a few weeks ago and it seemed to have great power (rear wheel spun out a bit coming up the driveway over the curb!), just coming to a stop sign is when the truck shakes violently and it will sputter if my foot isn't on the gas. I may rent a vacuum gauge this week and check for signs of vacuum leaks. I will also have to check what you guys suggested as well.

Thanks again.
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Old 05-09-2019, 08:42 AM
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definitely sounds like a vac leak to me. I would suspect EGR not closing fully or possibly the brake booster. disconnect or clamp off the brake booster line and see what effect that has. Also temporarily block off the egr with a piece of soda can where it bolts to the back of the intake plenum to rule it out.
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Old 05-09-2019, 04:40 PM
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EGR is certainly good to check as Melrose says. Also, I don't see "adjusted the valves" in your list, so I'd do that. And then also verify that your distributor is not off a tooth.
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Old 05-14-2019, 08:09 AM
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Hey guys I've got an update for ya. We had a mobile mechanic do an inspection on the truck for $80 and he found out that the first two injectors were leaking. He sprayed some carb cleaner while the truck was running and it revved up. So now I've got to get some new seals and 2 new belts. Hopefully I can get that done this weekend if the parts come in on time. Thanks for all your help!
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