Hello,
New member here. I have a 95.5 Tacoma 4x4 with the 2.7 engine with a 5 speed manual. For about three years now it would be running fine and then I would feel stumble that was very quick.Probably would not feel it with an automatic.The stumbles would slowly become more frequent and then it would die and would not fire. First time it happened I had it towed to a mechanic and he replaced the cap and rotor and everything was good again. I felt really stupid. Same thing happened around a year later and I replaced the cap and rotor and it started right up and ran well for about another year. The cap and rotor looked new. The third time replacing the cap and rotor did not fix it. There was still no spark. It got a new cap and rotor, plugs and wires, ignition coil and MAF sensor. It started up and idled smooth but continues with the occasional stumble not related to RPM, engine load or throttle position. I had a buddy look at it that said he thought he could plug his scanner into the diagnostic plug but it would not and he did not have an adapter. He did discover that the bulb for the CEL was missing. I checked all the grounds. I replaced the igniter for $501.00 and of course it did not get rid of the stumble. In the past when it began to stumble it would die in about 10 miles. Now it continues to stumble but not die. It is troublesome not being able to trust it so I don't get far from home and I carry my tow strap behind the seat I have no electrical testing ability and no one can plug into the diagnostic port except maybe the Toyota dealer. Also the cat was removed and replaced with a "test pipe" and made no difference with the 02 sensors plugged in or not. It was stumbling before the cat was removed and after the 02 sensors were replaced. I am running out of ideas and money. Would a bad ECU cause these symptoms? It is the only thing I can replace myself. I have not considered a fuel problem because of the speed of the stumble. The injectors were replaced a few years ago and based on the symptoms it does not feel like a fuel problem since it idles and runs smooth when not stumbling. Any ideas?

 

I would think that your Tacoma should have an OBD2 port somewhere. I have seen OBD2 ports on cars before '96, including a Lexus that was either a '93 or '94. I am assuming you are in the US? It might be different in other parts of the world. Being able to use a scan tool will be a big help in figuring out the problem without throwing money at it. The first thing that comes to mind is a crack in the intake hose. Air getting in after the MAF will be unmetered and cause stumbling if there is an intermittent leak. The hose probably got removed and reinstalled when changing the spark plugs and wires, so that could explain the change in the stumble after doing the wires.

Other things that come to mind to check would be the ignition switch and distributor. You can check to see if the distributor shaft is loose along with anything else inside that looks shorted or loose. Look for any marks inside the distributor that could indicate arcing where the spark is shorting out. The fact that the check engine bulb is missing tells me there is a mystery problem a previous owner didn't want you to know about, which is another reason to try and get the codes.

 

I think all should re- read my original post. I don't wish to repeat everything that I posted.

 

I have re-read your post about 4 times now and stand by my advice. What exactly am I missing?

 

It was the part about the OBD plug that you said that I should have. That is what I meant when I said "diagnostic plug" I said my friend's scanner would not plug into even with the adapters he has. As far as I know a scanner plugs into the diagnostic/OBD2 plug. I guess that I did not spell it out well enough? Also, I did not have any "changes in the stumble" you quoted. After everything that I have inspected or replaced with new nothing has changed. I guess that I should clarify "stumble" A better description would be a "tick" or "skip" It is so quick/fast/short that I guess it is not really a stumble. That is why I said that you wouldn't feel it if you had an automatic. At first I was puzzled because most of my driving is on gravel roads here in Kansas and I was not sure if I was feeling something the road was causing through the suspension or what. Once on asphalt roads that are smooth I felt it and then I could tell it was engine related. Once I put it in 4 low in first gear and crept it became much more noticeable. At higher RPMs and at cruising speeds it is more difficult to detect. I have put 165K on it and pretty much can detect new sensations and sounds.
Supernerd. I did not mean any disrespect. My key boarding is so poor that it is time consuming for me to type because of my arthritis and failing eye sight. Cataracts are a bitch at my age

 

I was assuming your friend's scan tool was an OBD2 code reader, since most are, and figured he could not find the correct port. There is likely an OBD1 diagnostic port under the hood that would not fit the OBD2 scan tool. Some cars before '96 have both ports with the OBD2 port under the dash. I guess I should have clarified that. I would recommend focusing on trying to get the codes read as that will save a lot of guess work and money. Even if you fix the check engine light, I am not sure if you can check the codes by shorting E1 and TE1 in the OBD1 port and counting the check engine light flashes. I think the early OBD2 diagnostic port replaced that method even before '96.

The changes in the stumble I was referring to was the fact that the problem went away for a year when you changed the ignition components.

I understand not wanting to re-type everything, and thanks for the clarification!

 

With the more specific explanation of the stumble, I am wondering if the ignition coil is not getting full voltage, therefore causing weak spark and occasional stalling.

 

Thank you for your reply the supernerd.My friends scanner is a OB 2 but due to the shape of the port it would not plug into the port located on the intake. He said that different brands of vehicles use different shaped ports to cause you to go to a dealer and use their unique tool. He tried his adapters and none would fit it. He was able to use pins and tap into areas of the port though. He removed the dash and found the missing bulb for the CEL. He swapped the cruise control bulb into the CEL socket. He also checked something under the driver side dash that was supposed to be for the inside the cab things? I did not understand everything that he was doing. I remember he said that the CEL must come on before a code would show on a scanner. He checked out the coil inside the distributor cap and said the primary or secondary was weak so I purchased a new one. He also checked fuses and wire connector plugs etc. His last thoughts were that I must have a poor ground somewhere You mentioned that the coil may not be getting enough voltage. What needs to be checked or how does one check the voltage to the coil and what would need to be replaced if it is not correct? I have replaced everything but the computer, or whatever it is called that is located behind the glove box. I am wondering if it could be something else inside the distributor? I have read about a pickup coil and a condenser as well as the gap between the distributor shaft and the condenser from great info. and illustrations provided on this site. I have not pulled the distributor and checked shaft play and other things suggested to check. Some of the out of spec. results were to replace the distributor body. I guess it is like setting the points gap in the old days. I still have my old timing light and dwell meter from the old days when things were simple. Also, what are your thoughts about the charcoal canister and or purge valve? Although I believe it is all electrical and not fuel related due to the nature of the "skip" I know I am jumping around a lot here but I did not mention that once it ran and I drove away the CEL came on about two miles down the road as well as the skip but again his scanner will not plug into the port under the hood.to read the codes. I also read on this site about a place one could send in your computer and have it rebuilt for $215.00 and have a lifetime warranty. I would like to know that it is the computer before I send it in. I may have to bite the bullet and take it to a Toyota dealer. I know they will insist that I replace the test pipe with a new cat right off the bat. The original cat began to rattle loudly and had some of the guts come loose. Removing the cat did not change anything about how it runs or any change in gas mileage. I have no change with the 02 sensors plugged in or unplugged either. Thanks again for all of your suggestions and trouble shootings. I wish I had more knowledge about all the electrical diagnostic stuff

 

The port in the intake is the OBD1 port, and he is correct that you would need a Toyota adapter for that. The more common OBD2 port should be under the dash, maybe he found that and there were no codes? More complex OBD2 scan tools will let you graph sensors and check misfire monitors which would be very helpful in seeing what everything is doing. There can also be pending codes where the check engine light does not come on, but the computer detects a potential fault.

Typically to check voltage at the coil, probe the positive terminal with a voltmeter with the ignition switch on and it should read close to the same as the battery voltage. If it is significantly less, then you most likely have resistance in the circuit going to the coil. What gets replaced depends on where the resistance is. If you are lucky, it is just a corroded terminal that needs cleaning somewhere. If it is an internal break in the wire somewhere it would need to be either replaced or cut and spliced.

I would not want to replace an ECU without knowing what the problem is. ECUs can go bad, but I think it is worth doing a full diagnosis before spending the money on that. Checking the distributor is worth a try. The play in the shaft could be done without removing it. Just wiggle the rotor and it should be tight. I doubt a misadjusted air gap would cause a light stumble, but it is easy enough to check. Check any wires in the distributor for anything obviously broken or cracked.

The evap system would basically create a vacuum leak. It would be easy enough to just plug the vacuum port on the intake port when the misfire happens and see if it stops. Usually vacuum leaks are less noticeable at higher RPM and more noticeable at idle.

You shouldn't need to take it to the dealer, just a trusted local mechanic. Some autoparts stores will check your codes for free, so that could be worth a try. The fact that the check engine light came on when it started to stumble is a good sign that there will be a code relating to the problem stored in the computer.