Low RPM rough Idle with bad acceleration

Hey all!

I am trying to figure out my issue with my 95 3.0 4runner. It starts fine then it rough idles at a low RPM and it has terrible and rough acceleration. I changed the MAF, distributor, plugs are good. Fuel pressure test is good so its getting fuel. It runs like it is not getting enough gas. Fuel filter changed as well. Gunna put in a new TPS as well since I have one, but any other thoughts on what it could be?

Thanks in advance all!

 

Definitely following to see if anyone has advice for you. I just bought a 1991 and the issue you're describing sounds like mine. The first thing I'm doing is fixing any electrical problems because it has a ton of aftermarket electronics causing a TON of parasitic drain. I'm hoping there's a bad ground. But I'm going to be looking at the intake into the throttle body as well. Maybe it's a vacuum leak?

 

Yea electrical is something I am worried about as well. I hope you get some answers! I took the throttle body off and gave her a good cleaning too. Forgot to list that in my initial post. Could be a vacuum leak. I actually dropped it off at my mechanic today (when i fail hahah) so he is testing that.

Ill keep ya updated.

 

Update my mechanic is stumped so far haha. He is going to take a look at electrical. He rechecked plugs, checked new distributor install, checked the TPS, Made sure the MAF was good etc.. Hoping to hear more soon. hope she is not a goner because there is only 136k on it!

 

So we got it idling well but now we get a code for the MAF but I put a new one in mid feb! Any thoughts would be appreciated. We put in a new ICM which helped with the idling but now acceleration sucks and MAF code. Maybe a faulty new MAF?

 

One thing that's easy to overlook is a leak in the intake tubing. My brother had a Corolla back in the 90's that was running like shit due to a cracked or tear in the tubing throwing off the MAF sensor.

 

Second on the MAF sensor & related connecting tubing, also look inside to ensure nothing is blocking the flow, Have seen leaves be wrapped up around the element and it caused all sorts of drive ability issues.

 

Thanks for the input! Ill take a look!

 

Question: For you rig what kind of engine air filter are you running? I ask because I learned about an engine code being thrown out pointing towards a MAF sensor but in reality it was simply because someone was running a K&N filter that was too heavily oiled thus restricting intake airflow. If you're running a paper air filter what condition is it in? Also check the airbox intake tube for anything that can be blocking airflow all the way down into the wheel well area. 0.02....

 

Thanks for

Thanks for the tips! I am just using your standard STP paper style filter nothing fancy. Filter is clean, but I am going to check the intake a little closer. I did not check in the wheel well area!

 

Did you buy a TOYOTA MAF? Or Denso? And NOT from Ebay or Amazon.

You simply can't trust anything else.

 

unfortunately I was unable to get a densco or oem one. There were none and the one I found online was like 600 bucks that was original. Also sorry for my lack of response I have been sick the last few months. 2 separate mechanics said they think it’s the ECU that’s bad so I found someone who is sending me one with my vin flashed to it. We will see I’ll keep ya updated! I know those aftermarket MAFs can have issues but after cracking open the old ECU it does have some burnt components.

 

$600 yowch.

I see Denso doesn't list it on their site. Sucks when cars get this old and parts get scarce.

 

I know. It sucks parts are so hard to find and the only ones available are cheap AF quality. My truck only has 136k so fingers crossed the new ECU does the trick .

 

Why was the original VAF replaced? Did it test bad? If you still have the original OEM VAF, test it with the attached procedure, it is an easy test and you only need a multimeter. If the numbers are good, there is nothing wrong with the VAF. After market VAF’s are usually very low quality components.

A vacuum leak could be the problem. There are so many sources of a vacuum leak on these old trucks the best way to check is to use a smoke generator. If your mechanic did not use a smoke generator, find a mechanic that has one or buy one from Amazon and check it yourself.

The distributor, ignition coil and TPS can also be tested with a multimeter. The Ignitor and ECM cannot be tested, but they are very reliable and usually do not fail.

Keep us posted with your findings.

 

Thanks for the info! The original
maf tested bad. I’m unsure how my
Mechanic tested for vacuu leaks but I’ll ask. He claims there are none but I’ll check on his method. Appreciate the input and I’ll keep ya posted. If the new ECU doesn’t work at least the company accepts returns! Also I’ll check the ignition coil but I think my Guys did that too.

more to come

 

Also am I correct that the ignition coil is under the distributor cap? Oh wait I think you said distributor, ignition coil

 

Also could be the crank shaft position sensor. Is that also located in the distributor? Trying to find info online

 

Whenever a crank position sensor starts going, usually starting the car is really hard.

 

Not saying this is your issue, but instead of replacing the ECU with another used one or whatever, there are companies out there that repair old vehicle ECUs. One such, ECUExchange is big in the older Mustang community. I had my 1990 Foxbody ECU sent to them (car ran fine, no 'real' reason to send it to them besides preventative measures), they ended finding a bunch of things wrong with it and fixed it all up for less than $200. Off the top of my head, some capacitors were replaced, a power supply wasn't outputting the correct voltage so that was replaced, they fixed some traces in the circuit board, did physical board repair, etc. These older 4runners are getting to the age where the computer components are just getting to the end of their expected lifespan and a refresh of components could be worthwhile.

I don't know if ECUExchange does 4runner ECUs, but its work a look for you, or anyone with an older vehicle.

 

Thanks for the info! Yea I found a similar company that sent me a ECU and I put it in with no luck. Still the same symptoms and a Code 12. Might be end of the line for the ole girl. I put in a new ignition coil as well.

 

Found this on Google:

"Code 12 Engine revolution signal missing"

Crank position sensor? Just spitballin here.

 

The RPM signal to the ECU is created in the distributor. If you did not have Code 12 before you replaced the distributor, I would suggest you replace the distributor, it should still be under warranty. If you had the code before you replaced the distributor, it could be a wire or connector issue between the distributor and ECU.

Here was the cause of my low idle RPM issue. https://www.4runners.com/threads/low-rpm-idle.44696/

 

Thanks for the info everyone! Yes we did a brand new distributor since we got the code 12 and it ran worse. sent that one back and got another and same issue. Runs better with the old one in with the code ironically. I found an OEM one finally for a good price so waiting on that to come in. The reason we thought it could be the ECU was due to 2 new distributors not fixing it but like we all know, the aftermarket parts are pretty cheap and not the best. Fingers crossed an actual Denso does that trick. Luckily not being charged an arm and leg for all this hahah. I usually do a lot of work myself but never really messed with replacing a distributor and do not want to mess up the timing etc...