Devilsven2

Hey ya'll, I'm new to posting but I'm really stumped about whats the issue with my pickup. I just bought the truck a couple of weeks ago and it seemed okay, I went from a 2004 tacoma to it so took a bit of practice but got it going. Over the next few days driving more, I noticed that it had a bit of a rough/ shakey idle especially after it was restarted, not as much on cold starts. I pulled the duct going from the air box to the throttle body and used carb cleaner to clean it, the throttle body, (open and closed), the airbox outlet and inlet, and the MAF. I also saw on a post about the idle control screw, especially about the oring around it and how they leak, so I replaced and lubricated it as well. I readjusted the idle to a comfortable level to my ear, and it sounded great, let it run for a bit, and all good, but the next day It had a similar problem, though it ran really well on cold start, (with a bit of gas) the second time I start it after It's warm, it shakes aggressively and I noticed the exhaust didnt sound right. Next I thought maybe ignition, I replaced the rotor and distributor cap but it didnt help much. Ive got a set of plugs I'll install next but I dont think thats it. I did the dollar bill trick and saw that the exhaust would pull the bill in, to me indicating a vacuum leak so thats what I looked for. I sprayed around with starting fluid on the vacuum lines, tightened the hose clamps on the intake, and didnt notice any leaks, but I did notice the dipstick was super loose and my gas neck was leaking when filling up. I replaced it with one that sealed well and got a new gas cap which solved the leak, but now the exhaust sounds similar, just more regular. Before it would sporadically make a sucking sound, now it sounds choppy almost like an aggressive cam LS. I've also noticed a loss of power since I bought it, not major but a little bit, as well as possibly worse fuel efficiency. I've seen some things about the gear-tooth adjustments in the MAF sensor, as well as o2 sensors and egr valves, but before I chase everything and throw money at it I wanted to see if anyone has any advice. Also, my tach is not really reliable so I've been relying on my ear and watching my shifter. Thanl you fro the help in advance.

2ToyGuy

Do you mean the one integral to your truck from the factory, or an external one? I bought a $10.00 cheapie back in 84 when I bought a Chevy Luv, that had points. It is still working quite well. The meter, not the truck. Very accurate. Harbor Freight special, I think. Did HF exist back then? I bought a timing light at the same time, and IT is still working very nicely as well.
It doesn't take a super expensive piece of equipment to perform adequately and for a long time.
If you mean the one in the combination meter, with the fuel gauge, speedometer, and so forth in it, yes.Those aren't known for their excessive accuracy, but should be adequate for getting you at least close.

As for your main problem: Have you tried clamping off the tube from the IACV when it's good and warm and seeing if that has any effect? If so, check the IACV for proper operation, and ensure it's still clean inside.
Also, have you tested the EGR valve according to the FSM? Another very good possibility. They get clogged up with gunk from the exhaust gasses, and stay open when they should be closed at idle.
Same with the PCV valve. Check that it opens and closes properly. HOWEVER! Be very cautious removing it if it has been installed any more than a couple of years. The grommet it's in get's brittle over time, and when you go to remove the PCV, it can disintegrate and fall down into the valve train. A pretty good idea to pull the valve cover off before you try to remove the PCV. If nothing happens, no loss, and you can set the valve lash. If the grommet disintegrates, you don't get bits and chunks where they don't belong. If the PCV needs replacement, get an OEM version from someplace like Rock Auto, or your local dealer. Do NOT get some chain store plastic cheapo version. You'll regret it if you do.
Good idea to replace the valve cover gasket and it's 2 halfmoons while you're there. About a $20.00 set, and very easy to do.

Did you pull the idle adjust screw and check the o-ring on it? They also get old and brittle, and if they come apart, small chunks can fall down into the air passages the IAS controls. Remember, it's the smaller screw under the large cover screw on the left of the top of the throttle body, as you face it. Not the larger, cover screw. Make sure you screw the IAS down until it bottoms out, counting turns carefully. It will give a decent starting point if you have to replace the o-ring. The o-ring is small, and readily available in many places where auto parts and hardware are sold.
It's a good idea to wipe a thin layer of Vaseline or silicon dielectric grease on the o-ring before you install it. It helps it seal better, and it makes the rubber last a good deal longer than without.

Do you have a Check Engine light? If so, have you pulled the codes for it? Those might give you a starting point, at least. Especially, say, for instance, the code for the O2 sensor. Quick, easy replacement, if the bolts aren't corroded into a mass of rust. Do NOT use Bosch. They're made for European cars. Use Denso or the like ONLY.

When you replaced the distributor cap and rotor, did you think to replace the plug wires? All 5 of them. 4 for the plugs, one from the coil. Again, only use OEM wires if possible.
Yes, also definitely replace the plugs. Check the gap before installing each one. They may, or may NOT be gapped correctly from the manufacturer. Once again, use OEM plugs. Denso or NGK plugs. They work better than most others. Don't overtorque them!! IIRC, 13 in/oz is the right torque, but check me on that. I may well be wrong. I KNOW it's 13 something, but I can't recall for sure if it's ft/lbs, or in/oz.

Did you verify the exhaust gasket, between the head and the exhaust combiner? If it's leaking, you can feel it just by getting your fingers close once it's warmed up. You'll feel the warm air. DON"T TOUCH! VERY hot!
Any loose nuts or bolts where the exhaust piping comes off the head? Easy to check, when it's cooled down all the way. Like overnight.

OK, my brain hurts now...
Good luck!
Pat☺

Devilsven2

Thank you so much for your detailed reply, I seriously appreciate the effort you put into helping me!
Regarding the tach, I was talking about the OEM tach that is built into the gauge components, Like I said its sometimes accurate sometimes not, I think ill to go out and look into a timing light for diagnosing issues
I haven't blocked off any tubes coming out of the IACV, actually, I didn't even know it was called that until just now, I can definitely do that, and to confirm it is clean I'll take a look, or do you recommend taking it off and disassembling?
Also, I have a factory service manual from Chiltons that came with the truck, I'll see how to test the EGR, I've heard a lot about people having issues with them and deleting them, I would rather not since I'm in California and I'd like to keep it smogged. This makes me pretty hopeful I can clean it out instead of taking it out lol. About the PCV valve, I was talking to a friend and he suggested that may have been the issue, so I attempted to remove it but it was stuck pretty tight in the valve cover, and I was aware of the risk of breaking it so I let it be, Ill try that if nothing else is working, a good idea to remove the valve cover, I've already bought the gasket for it . I did pull the idle adjustment screw, and the Oring was brittle, I removed it, changed it to a silicone one, and lubricated it with some dielectric grease. I haven't gotten any check engine light, although I'm suspicious it may not be working correctly, just my internal worry tho. I didn't know you could pull codes from it, I'm curious what tools are required, since I'm aware obviously it doesn't have an OBD port, I'll do some research and see it I can do that first. When I bought the truck, I noticed that the plug wires and coil had been replaced very recently, so I didn't bother replacing them, I am wondering now if they were trying to fix the same issue. I'll see what I can find about pulling codes, and since I have them I will go ahead and do spark plugs, and just for my knowledge I'll do a compression test at the same time. Again, thank you so much for the help!

2ToyGuy

Tools needed for pulling the codes: paper clip, or a short piece of wire to make a jumper out of. And your ignition key, of course.
There is a test connector right on the fuse box in the engine compartment. Small box, plaastic, with a top that opens up. Once the top is open, it should have a diagram in it of what pins are labeled what. You'll wat T and E1 jumped. Then, get behind the wheel, and turn the key to ON. The CE light will flash. Count the flashes to get the code. Like if it flashes 3 times, a pause and then twice, that code 32. If it just flashes over and over with no pauses, like flash, flash, flash, etc, that indicates no code to read.
Check the FSM for what each code, if any, indicates.

It's a good idea to clear any stored codes you may have, to keep from chasing a trail that's already been repaired. I pull the negative lead off the battery to clear the codes, but ou can also pull the EFI fuse out for two minutes. Once the codes are cleared, run the truck until the problems happen again. Twice. The CE system won't trip a code unless the same problem happens on two separate operations of the truck. Two different trips to the store, for example. They call it "two-trip logic".

The CE light should go on, along with all the other idiot lights, when you go to start the truck. If it doesn't, you may have a bad bulb. Quick, easy check to ensure the CE light is working properly.

Good luck!
Pat☺

old87yota

This truck is a 1986 model and likely has the diagnostic connector to pull codes on the driver's side by the ignition coil on the inner fender. Toyota switched to the integrated diagnostic connector by the fuse box during the 1987 model year. Your diagnostic connector is one of the round connectors that doesn't connect to anything and should have a rubber cap on it.

You would still jumper the terminals.

I don't remember which one it is though.

2ToyGuy

My apologies. I was going by what's in my trucks, both 87's. I thought they were the same, 86 to 88. Apparently, I was mistaken. Yeah, that's what I get for thinking

Again, I apologise.
Pat☺