"I've got a slight mis-fire when I hold the engine at 2,000 to 3,000 rpm"
This is a question I get at least 2 times a day, and sometimes MUCH more.
Usually shows up when the engine is at normal operating temp. If you are sitting still and hold the engine around 1500 to 2500, there is a slight “miss”, kind of in a random pattern. It may also show up while at cruise speeds in that same RPM range, although it’s a little less noticeable due to road noise and vibration.
WELL!!??? What causes it?
It’s all your fault. Karma. Remember when you tore the wings off of that fly back in 3rd grade? Yep, it’s because of that.
Either that, or one of these many reasons listed below. Don’t skip any of these along the way, each one needs to be checked.
THE EASY STUFF FIRST
Check the easiest goodies first. Those janky aftermarket plug wires? Make sure the ends are fitting all the way into the distributor cap and are snug on the spark plug side. Any cuts or abrasions ANYWHERE on the wires is a potential place for failure. Pull the spark plugs and check the gap, check for wear.... and make sure they are Denso or NGK. None of those German platinum or "650 billion VOLT, multi-electrode X-TRA spark" shenanigans you ordered off the internet after seeing them on some hillbilly car show you saw on a Sunday morning. Check the valve adjustment and keep an eye out for any that are too tight. We recommend checking valve adjustment every 10k to 15k miles.
THROTTLE POSITION SENSOR
It’s a big deal. You can’t just wing the adjustment, or assume that it’s good, it’s one of the most important inputs to your ECU. It has to be functioning properly both mechanically and electronically.
Follow this link for step by step instructions: TPS TESTING AND ADJUSTMENT
Everything checked OK? Move along to the next thing.
Since you are a responsible 22RE owner, I know you have this right. But, let’s bring it up just to make sure we are all on the same page.
*ALL OF THESE RECOMMENDED TIMING CHECKS / SETTINGS ARE VALID AS LONG AS YOU KNOW YOUR TPS IS FUNCTIONING PROPERLY. YOU DIDN’T SKIP THAT SECTION, DID YOU?*
Base timing should be at 5 degrees with the ECU “jumped” and 12 degrees without (of course after the engine is at normal operating temp). ALWAYS check your timing with a timing light and follow the procedure shown in your manual.
There was an internal bulletin for Toyota factory technicians back in the mid 80’s about a similar issue with 22RE engines. The issue was an internal programming problem with the ECU. Since the ECU advances the timing according to engine RPM, throttle position etc., sometimes it would freak out and give it too much TOTAL advance on accel and partial throttle. It would give it 40+ degrees total advance instead of the 28 degrees (those are random numbers I pulled out of the air, not the ACTUAL numbers, just using them as an example). For a while during the time when owners of these trucks actually brought them to a dealer, one of their fixes was to install a reman ECU (that’s why you see some of the ECU’s in the 85-87 model years have a “-84” after the part number on the sticker, it means remanufactured). It didn’t always help.
One fix that was recommended in another, later year, bulletin was to set the base timing at 3 degrees instead of 5 (which would translate to 10 degrees without the ECU jumped). If that didn’t help? They recommended 2 degrees base timing. I know it sounds counter-intuitive to retard timing to improve performance, but about 50% of the time, it would solve the problem.
Even though I’m using the 85-87 model years as an example, I’ve used this method to fix the problem on trucks all the way up to 1994.
Ok, here we go.
The quickest way to eliminate a potential problem with your EGR valve is to take it out of the mix completely without having to remove it from the engine. Here is how by-pass it for diagnostic purposes.
Loosen the 27mm nut at the egr pipe, the loosen the two at the egr pipe to plenum. No need to fully remove them, just back them out a few threads, just enough to allow some room between the pipe and gasket/plenum. Cut a piece of aluminum can as shown in the middle picture above. Slide it down into the gap to cover the EGR hole at the pipe (again, shown in the middle picture). Tighten up the two pipe to plenum bolts and the egr pipe nut.
Road test it. Gone? No more miss? Good. Either the EGR valve is leaking exhaust gasses in to the plenum (creating a vacuum leak/lean run condition). You'll either need to clean or replace the EGR valve.
“My truck cranks for a long time before it starts when it's cold. I need a need a new COLD START INJECTOR!”
Ummmmmm, probably not.
how to check your thermo time switch
Do you have trouble starting your truck in the morning? Long cranking time before the engine starts? How about after it’s sat for a couple hours? Most people seem to think it’s their cold start injector. Kinda’. More than likely the cold start injector is not “turning on” (making you think it’s bad) due to the thermo-time switch being out of range.
It’s a pricey part, so I recommend you check it before I sell you something you may not need. Grab your ohm meter and let’s do this.
This test should be performed when the engine is COLD! As in, it’s sat overnight COLD.
Connect the probes to the pins in the THERMO-TIME SWITCH.
1984-1988ish BROWN, SQUARE connector (shown at left) should read between 20 to 40 ohms when coolant temp is below 77 degrees. If you are getting anything higher than 40 ohms (when coolant is COLD), the thermo-switch is out of range and is not turning the cold start injector on. It
1988ish-1995 BLACK, ROUNDED connector should be 30-50 ohms when coolant temp is BELOW 50 degrees (yes, 50, very cold). If you are getting anything above 60 ohms when cold, the sensor is out of range.
When the sensor fails it usually fails in the “engine hot” range and it’s giving the ECU the wrong signal. When this tells the ECU the engine is already “hot” it doesn’t turn the cold start injector on, causing the long cranking time and rough idle when the engine is cold.
If you are getting the correct readings, but are still having the issue, check the condition of the wiring harness that connects to the switch. Because of the severe bend that it takes in combination with the high under-hood temps, these wires tend to get brittle and cracked. Take a close look at them and make sure everything is groovy there.