Sam Latone

Ok guys, after reading 15 threads about rough idle, none of them seemed to guide me in the right direction or offer a resolution to the issue.

87 4Runner bought a few months ago. Put close to 1500 miles on it since purchase and the 22re has performed flawlessly. The motor usually idled at 900rpms very smoothly.

Today at a stoplight I noticed the idle bog down to 600 and go up and down between 600 to 650. During this time the car shakes noticeable. I smelled what smells like rich exhaust or burnt oil(not sure) begin coming from the exhaust. The exhaust note is odd at idle, like a popping/sucking noise that is not steady or consistent. During a cold start the motor idles great at 1100rpm but after 3 minutes the idle comes down and does the 600-650 rpm loping idle. When you rev the motor above 1000rpm the exhaust note becomes normal and then shaking goes away. Under load the car tends to hesitate coming up off idle until it's around 2000rpms and then it seems to run fine.

The issue was a very acute onset which made me consider that it was electical in nature. I replaced the plugs, wires, dist cap/rotor, coolant sensor

Another thing I noticed(may not be related) is that shortly after the rough idle and bad exhaust smell, I noticed that the tach started bouncing all over the place giving inaccurate readings. As I would smack the dash the tach needle would jiggle and then it just quit and began working normally again. During this time I also noticed the temp gauge needle giving a middle reading, then dropping all the way down, and then coming back up to the middle(operating temp).

I replaced the coolant sensor thinking that could be causing the bad reading on the coolant temlp gauge as well as the rich condition after warming up but it didn't do a think and neither did the tune up.

Thanks in advance guys!

coryc85

Check for vac leaks, missing or cracked vac lines.

Co_94_PU

iTrader: (-1)

You didn't find a single resolution because there isn't one thing that causes these symptoms. It is one of the more simple systems but there are still several sensors involved as well several mechanical devices.

Do the simple quick checks first. The vacuum lines. A good benchmark is the hoses are firm and tight and do not rotate on the fittings easily when you apply torque. They should also be soft/supple and crack free.

The coolant level should be right to the top of the radiator, the resivore is above the minimum mark, when the engine reaches operating temp the resivore level should rise slightly and when it cools off it should return to a lower level (IE the radiator refills from the resivore). If the seal on the radiator cap is dry cracked or just overly compressed it will induce air to the system, if that air makes its way to one of the coolant sensors or the air valve under the intake you will have an erratic idle(it's pretty common).

Exactly which "coolant" sensor did you replace? There is the one horizontal at the front of the intake, another (or several) on top of the thermostat, and the one for the dash gauge located in the middle of the lower intake next to the block.

Have you done the brake booster checks? From memory.. start with the engine off, depress the brake pedal, while holding the pedal start the engine the pedal should move towards the floor, release the brake pedal and press it to the floor again the idle should breifly climb 50-100 rpm, press the pedal to the floor then turn off the engine the pedal should not move farther towards the floor. If it does not display these characteristics it's faulty.

The gauge cluster is old and has been subjected to lots of vibration from the engine running as well lots of jolts from potholes and curb thresholds. It's almost certainly time to retighten the screws that make up the electrical connections on the flexible circuit board. Once the screws come loose the copper will oxidize and require cleaning. In some cases there might be physical damage to some of the coil wires.

Methodically go through the diagnostic flow chart and post the results and the community will happily try to help, but you will have to put in the labor.

RAD4Runner

Like Cory85 and Co_94_PU say ^^^

EDIT: Temp sensor on top of thermostat housing is some sensor to shut-off air conditioner in case of overheating... (earlier error, I said it is for the temp gauge)
The coolant temp sensors that could affect idle are below. No need to replace unless tested bad; Just need to clean thoroughly at least once every 30 years Pls see my thread to see how I know.


Right to left:
CSI timer switch, Bimetallic Vacuum Switching Valve (EGR control), ECU temp sensor

Sam Latone

Thanks for providing a starting point! I will run the truck through the proposed checks/tests and post ASAP. I'm currently in a very time consuming and exhausting job training program so it may take a bit. Thanks for the help.

L5wolvesf

I don't know if this is related to the idle issue but the paragraph I quoted aboue reminded me of this thread:
https://www.yotatech.com/forums/f116...ge-fix-271152/

Hope it helps

RAD4Runner

Like Co_94_PU says ^^^. My cousin's Civic exhibited same symptoms. He found a crack on radiator which we think sucked air in.
When there is air in the system and air bubble surrounds the ECU temp-sender, ECU will get wrong temp readings.
If air bubble surrounds the temp gage sensor (an to of thermostat housing), you'll get erratic reading. On my truck, I was reading low temp on the freeway. Turns out I was losing coolant because of bad HG before it actually overheated.
Maybe try burping the cooling system?