My sub idles smoothly but stumbles during acceleration. I've changed plugs. No dash lights indicate problem. Haven't touched the timing belt. Not bad gas? What should I check first, second....? Thanks!

Plug wires. At least for me. Fixed it. Get Subaru ones for best results.

Hmmm when was the last time it had a tune up...perhaps a clogged fuel filter...perhaps a bad sensor its hard to tell sometimes....any maintenance history? automatic or manual? How many miles are on the vehicle? Usually if you have an open plug wire it will cause a miss and throw the light...however I do know for a fact some of the early subarus where hesitant to throw the light even though they where OBDII..I have actually seen some older Subarus miss like you wouldn't believe and the CEL never illuminated...and yes the light was working properly..lol...Also check the ignition coil...

My sub idles smoothly but stumbles during acceleration. I've changed plugs. No dash lights indicate problem. Haven't touched the timing belt. Not bad gas? What should I check first, second....? Thanks!

 

1 fuel filter

2 wires

Thanks for the advice. I'll try plug wires and fuel filter. (Actually I have 2 of these 98 Sub Legacys so I'll do a little parts swapping to troubleshoot). BTW, regarding maintenance and more details...it's a manual, 97k miles, I replaced the clutch, and other mechanical parts during the clutch repair, and have replaced the air filter. I'm the 2nd owner. Would it be sensible to swap out the EGR? Thanks for your comments. I'll let you know what I learn.

Would it be sensible to swap out the EGR? Thanks for your comments. I'll let you know what I learn.

 

No

OK - new plug wires and fuel filter and no change still rough on acceleration. Could it be injectors...? Any suggestions are welcome! thx

My bet's on a Vacuum leak. Check the hoses for cracks and dry rot. Replace any that are hard, brittle, or feel loose on the nipple they're attached to.

"new" or "I got them from subaru yesterday" new. Unless they are the later I wouldnt say it hasnt been diagnosed. Also you need to do a real tuneup, plugs, wires, filters, CV valve.

 

This being a 1998, it may be overdue for a timing belt. On a 2.2 it is every 60,000 miles (1 month = 1000 miles) With it being such low miles the 2nd timing belt may past it's life, assuming that the first one was ever replaced. Check the timing belt.

 

 

nipper

Edited February 15, 201016 yr by nipper

3rd. Confirming adequete fuel pressure would be worthy before diving into deeper subjects like the MAF and TPS.

look into the coolant temp sensor

Thanks for the comments and advice - I'll try the vacuum leak and fuel pressure. The wires were new, as in new yesterday, not swapped (I presume you may have assumed I swapped em from my other sub??) Belt was changed at 75K Naru, what's MAF and TPS? Thanks!

Thanks for the comments and advice - I'll try the vacuum leak and fuel pressure. The wires were new, as in new yesterday, not swapped (I presume you may have assumed I swapped em from my other sub??) Belt was changed at 75K Naru, what's MAF and TPS? Thanks!

 

MassAirflowSensor and ThrottlePositionSensor

 

Look at the CoolantTemperatureSensor before those.

 

Vacuum leaks normally result in poor idle quality.

(greater charge dilution at lower airflow)