‘94 won’t pass emissions but NO CEL

[109madrid]

I drive it here and there but lately I’ve been avoiding driving it to prevent further damage, mainly because until recently I wasn’t sure what was going on around the lean condition/code 25 -can I drive it on a couple hour trip on only 5 cylinders safely? Do I disconnect the injector or anything, or just let it ride? I drove it on a 100 mile/2 hour round trip recently and it did 80mph on 35’s up the hill to Santa Fe (which is a big “hill” at elevation) but the trip prior, I could feel that cylinder lagging/the intermittent miss and could only do 55-60mph up La Bajada/the “hill”. If you know the “hill”, clearly only a healthy LC motor can do more than 65-70mph up it.
At this point I think it’s a bent valve or a burnt valve because the problem is intermittent and sometimes it runs perfectly and then will have a totally random stumbling idle. The motor only has around 40k miles on it so I don’t think that it’s an issue with carbon buildup and it’s a new Toyota short block because I have receipts from the PO but do not know if they reused the head from the old motor (head gasket failed at around 200k) because it was the previous owner who did the work. It was a shoddy job because when I got it it would stall (but it passed emissions for a several years) and I found out that they reused the sensors from the previous motor and broke a lot of them when they reinstalled the engine (both knock sensors were smashed up but still plugged in, lol). Once I replaced the broken sensors shortly after I bought it, it was perfect for several years and then started doing the code 25/26 combo and here we stand.

 

[Dave 2000]

This is one of those 'how long is a piece of string' questions.

Short block means nothing in this scenario. A bent valve would mean the misfiring at idle would always be there, as would a burnt valve, a gummed up valve on the other had will actually cause the misfiring to come and go, valves tend to rotate when the engine is running, and the gum could be sticking in one area and not the other?

If the valve does stick down (gummed up valve stem, bent shaft, broken spring, burnt valve, ect) then you run the risk of it sticking down or even breaking up and being clouted by the piston. FWIW and assuming a spring has not broken (rare in my experience), there is something else you can try but with care.

Keeping in mind that the effort to close the valve is nothing compared to a cam lobe pushing it open, remove the spark plug and rotate the engine until one valve is fully open, then using one of those 360 degree spray attachments used to spray rust treatment into car body cavities, shoot something in the chamber, give it a good drowning to loosen and clear any gum on the valve stem, in the UK it was called 'Red X upper cylinder lubricant' and it is brilliant, you or other MUD members may know of something else that dissolves hard deposits on valves. With the cylinder having been given a good flooding two or three times leave overnight, if you have the time then do it again the following day and leave overnight again then all the better. Repeat with the other valve.

Note! When you have finished spin the engine with the spark plug still out and the coil lead/s grounded. This will eject any of whatever product you used, failure to do this you could do more damage to the engine. Usual disclaimers apply here.

Replace the spark plug and away you go and see if anything has improved, there will be some smoke when you first start up. Whilst I am an old school mechanic (50 plus years), I have managed to keep up with the tech stuff, but sometimes old tricks are more than useful, good luck.

Regards

Dave

 

[109madrid]

Thanks for the direction here, I appreciate it especially those insider tips. Hopefully it is just gummed up, and it is definitely intermittent because it idles perfect sometimes for days at a time and it always makes me think it’s fixed and then all of a sudden it starts randomly stumbling at a light. I thought my belts were whining too and for some reason when the idle smooths out, any little squeak/whine from the belts goes away too. It also used to do that common rattle noise upon startup and I assume that when the valve rights itself, the rattle upon startup is goes away as well. As you can see, everything looks fairly new so I’m hoping it is something like a gummed up valve, I will try cleaning the valves and see what happens

 

[Dr Red]

So what was the final verdict here?
My 93 stumbles at idle, has a CEL that comes and goes, and is throwing a code 25.

 

[109madrid]

My local independent Toyota shops refuse to work on it because they “don’t have time for a head job” (sounds like the wife lol ) nor do they have time for sending it out for the associated machining. The 2nd shop I took it to said it had 30 PSI in cylinder #5 and told me that I had a burnt valve and that the head gasket seems intact because it’s not leaking air into the coolant (2nd shop that confirmed this). I scoped it and contrary to what the shops are saying, the valve does not look burnt at all, but completely gummed up. The spark plug is also not looking as if it is running lean as a burnt valve would show but I haven’t had time to work on it and would love to do what Dave 2000 recommended previously but have very little time to do anything at the moment. Here’s a scope I took to show the condition of the valves, please chime in if they look like something more than a gummed up valve is wrong…