I have an 85 4Runner that I bought a couple of months ago. I have put about 1000 miles on it. I recently filled up the gas tank after driving on the freeway for 40-50 miles and as I was pulling out of the gas station the truck started running really rough. I drove it about 1 mile and decided that I shouldn't drive it anymore until I knew what was going on. I tried to start it 3 hours later and it wouldn't start. I tried to start it a couple of days later and it started...it still ran rough, but I was able to get it home.

I asked a mechanic friend for his opinion and read lots of online posts...my first diagnosis was that it may be bad fuel. I put some Heet gas additive in there and that didn't make much difference. I changed the fuel filter and it ran like a champ...more power than it has ever had.

After about 70 miles on the freeway it started running rough again. It was nowhere near as rough as when it first had trouble right after I filled up the tank, but I pulled off the freeway and called a mechanic friend. He said it may be corrosion in the tank (the 4Runner has 300K miles). After I let it sit for 20 minutes I jumped back in and it ran like a champ for 5-6 miles, and then started to run rough. It continues to run well for 5-10 miles and then it runs rough until I let it sit for a while.

I am going to drain the gas tank and see what the fuel looks like. I also rented a fuel pressure tester.

Has anyone had a similar problem or know what might be going on? Thanks in advance!

 

I stopped by autozone today and asked the kind gentleman if he could help me read the codes for my check engine light (engine light only comes on when the engine is running rough). When he saw my 4Runner he looked at me like I had just kicked a puppy. He said he could only read 95 and newer.

I drove to a shady spot and looked up 4Crawlers instructions for reading the engine codes. I pulled the codes and got the following:

#3...No signal from the igniter 4 times in succession
#6...No engine revolution sensor (Ne) signal to ECU
#10...No starter switch signal for ECU w/vehicle speed = 0 and engine RPM > 800
#12 Knock control sensor (KS) signal has not reached judgement level in succession

HUGE THANKS to 4Crawler for all his help! http://www.4crawler.com/4x4/CheapTri...html#Early22RE

I am going to reset the ECU and see what shows up the next time that I drive. My guess is that it isn't the fuel system, but something in the ignition.

 

After I reset the computer and I drove it for 7 miles it started running rough again. Codes 3 and 6 showed up.

I drained the gas tank to see if there was any corrosion or junk in the gas tank. The gas looked good and I didn't see any signs of corrosion (particles or discoloration).

I also changed the fuel filter again to see if it would run well for a while after changing the filter. Last time I changed the filter it ran AMAZING for 70 miles and then ran rough. This time it ran well for about 5 minutes and it started running rough again.

Any thoughts on what is causing the 4runner to run rough would be appreciated! Thanks!

 

I have been working with a professional mechanic to try and diagnose the issue. He worked on it for a while and said that he thought it was the distributor. I just changed the distributor and unfortunately, it didn't fix the problem. It ran well for about 5 miles and then it started running really rough again.

When my 4Runner is running rough, it runs a little better at 3-4K rpms, but the tachometer is still going all over the place...sometimes the tach surges from 2K to 7K without the engine actually surging. Often when it idles it dies, but I have no problems starting it again. As long as I give it a little gas, it runs okay.

It seems like the warmer the engine gets, the worse it runs. When the problem showed up initially I had just pulled off the freeway after a 40-50 mile drive. When I pulled out of the gas station it started running REALLY rough. I am assuming that the engine would be the hottest after a long drive and then stopping for a minute. It didn't start for a couple of days after that gas station incident, but after that it hasn't ever had problems starting again.

Any suggestions would be appreciated!