I have an 1987 Subaru GL 1.8 5 speed. Last year I had an issue with the car stumbling when I tried to accelerate. At that time I was able to disconnect some of the hoses going to the air cleaner, plug them off and fix the issue. It was probably a air leak or clogged hose. I ran the car fine all summer but now it appears to be happening again, this time slightly different though.

 

When the car is cold it happens but this has always been the case and it goes away when it gets a bit warmer. Now, after it warms up it runs great for about 10 minutes drive time, accelerates great, pulls up hills without hesitation, etc. However, the problem then begins to start again.

 

It idles great but when I try to put it under load it stumbles, almost backfires if I give it too much gas. I'm thinking there is some pressure building up in the system that is not being released and that is what is now causing the problem. The EGR valve is not it since I have the same issue with it connected or not, I don't think it has ever worked honestly. 

 

I'm wondering it the vapor canister can have this kind of effect? Is there another valve somewhere that could have this effect? Any idea's would be appreciated!

The O2 sensor is a pretty common cause of bad performance like what you describe.

IF it is a SPFI, first thing to check is the CTS.  The 2 wire sensor on the thermostat housing.  They fail in odd ways that do not cause the CEL to light, or even register a code.

 

They do cause all sorts of drive-ability problems, sometimes intermittent, sometimes engine temperature dependent.

Could be a bad spot in the TPS also if it's SPFI. IMHO they seem to fail at 250k miles or so.

Edited November 5, 20178 yr by Crazyeights

I would guess the coil is bad

When trying to diagnose engine performance problems, an easy test to perform is a vacuum test.  You can learn lots from it.

 

Reconnect any altered hose connections, then run the test.

Hitachi carb?

Hitachi carb?

If it has an hitachi carb it could be the accelerator pump not working / spraying fuel  properly.

Or maybe an ongoing vacumm / air leak somewhere as you mentioned

 

As this is is an intermittent fault,  agree also,   it could be the ignition coil.

Coils  do funny things like cause intermittent problems when failing,    especially when / after coil warms up, and especially under load.

Edited November 6, 20178 yr by subnz

Doubt it's an o2 sensor. double check your vacuum lines. i'd guess it's the coil too

Cripes!! How about OP tell us what he has got and what he has replaced if anything otherwise everyone sort of wastes efforts if it is carb, if it is spfi. The net is full of people asking questions without completing story and tangents are created. Not knocking anybody mind house

 

The netwzves be more peaceful if when you get problems with the tune of your jalopy go whole hog and buy new spark plugs, leads, coil,cap and rotor, points and condensor if fitted, then come back in. Some fuel cleaner doesn't hurt a tank before new fuel filter either.

 

Steps off milk crate....

I appreciate the replies. It is a 2bbl carb, not sure if Hitachi or not. I replaced the coil last year since I was thinking it was that the last time this happened. I do believe it is another vacuum leak that I need to track down. I was able to plug one hose and it did help a bit so I need to spend time tracking the connections down and checking for leaks. 

 

Again, thanks for the input.

That stumbling before the car taking off was very common when I had a Hitachi carb on my 86' 4WD 5spd. Drove me nuts. I had the carb rebuilt but it was of no help.

 

Dump the Hitachi and put a Weber on it. It will make all the difference. There will be a several vacuum lines you won't need with the Weber so that right there will avoid vacuum leaks. The Weber will give the car more power. You'll think the cost is too high to change to a Weber but over the long haul of driving the car you'll be glad of the investment.

 

http://www.redlineweber.com/carb-kits/

Carburetor icing can be a problem at this time of year.  Is the air heating system on the air filter intact, or did it get removed last summer along with the vacuum hoses? 

 

Usually, this shows up at speed, with less and less power available, more throttle required, until you have to pull over.  It goes away when you pull over and wait for a few minutes, while pulling your hair out trying to figure out what is wrong.  .  But the 10 minutes driving fine, until it shows up, makes me wonder if this isn't what is going on. 

I appreciate the replies. It is a 2bbl carb, not sure if Hitachi or not. I replaced the coil last year since I was thinking it was that the last time this happened. I do believe it is another vacuum leak that I need to track down. I was able to plug one hose and it did help a bit so I need to spend time tracking the connections down and checking for leaks. 

 

Again, thanks for the input.

Yes, it is a vacuum leak, most definitely. I know that exact symptom. Step on the gas and nothing much happens for a fraction of a second, a dead spot in the acceleration. Good luck in chasing down that leak. It's not worth your time, the Hitachi carb will always suck, in one way or another.

I think I have figured out the item giving me the problem, it's the Air Control Vacuum Valve. I noted the item number on the part, Hitachi SPDL30-21. The c=valve has 3 hoses connected to it, 2 on top, one on bottom. The bottom piece broke off so now it is no longer connected. I capped the hose and put a temp cover over the hole in the valve and that seems to almost fix the issue, still happens on rare occasions, not like before.

 

So, I need to replace this piece but I can't find one online. I may end up trying to glue it back together if I can't find one. Any idea's where I could obtain one, or does anyone want to sell me theirs?

 

Here is a pic I took from another users post....

Mate are you still chasing the part ? I just found one in my shed.

 

 

If you still want it send me your addy and its yours.