1994 16v Sidekick stumbling at low throttle

[Zerva5]

Hello! I've been trying to diagnose this annoying issue on and off for a few months now. The main symptom is at low throttle the engine seems to stumble and recover, stumble then recover, which results in the car jerking forward every time it recovers. I would say it repeats this stumble recover cycle repeats a few times a second.

At first I thought it was EGR related. It passes the stall test however during the live test the EGR valve wasn't moving. I also saw that the idle was very smooth and there was no stumbling. After doing some research I concluded that my sidekick was one of the ones in 1994 where the wheels needed to be spinning for the EGR to engage. I didn't have access to a jack at the time but I tried lightly revving it in neutral while stopped as well as while moving and found that it wouldn't stumble when I wasn't moving but would stumble when I was coasting.

Today I was able to use my buddies jack and did the live test which it passed. Interestingly even with the wheels spinning I wasn't able to make it stumble revving it in neutral. I was also thinking it may have been ECU related and that the VSV was opening and closing and making it stumble. I didn't hear any clicking from the VSV or ISC solenoid so I ruled that out for now.

My buddy is buying a used engine that has a MAF sensor I'm going to throw on and see how it goes. The engine also sounds like it is misfiring a bit at idle. Nothing too bad however.

Things I've checked/done:
VSV: Blowing through it and with 12v
EGR Main: cleaned it top to bottom
EGR Diaphragm: Checked for a clog, there was one, unclogged it, didn't change anything
TPS: Replaced with a used one and calibrated it, no difference
Spark plugs: Replaced
Air Filter: Very clean
MAF: Its clean, didn't check anything else


What I'm planning to do:
Distributor Cap
Distributor Rotor
Plug Wires
Fuel Filter
Check for vacuum leaks
Change timing belt & water pump

I'm not really sure where to go from here, I have an entire used intake I was thinking of doing a deep clean on and swapping in but wonder if you have any other ideas.

Thanks!

[jwunsch]

Is your hot idle stable 800 rpm and if you load the engine.. say blower full, high beams, window heater etc and it recovers to 800rpm.

If not I would diagnose the ISC. Mine is dead and previous owner has done some dirty tricks to get hot idle around 800rpm with high beams etc its 650 and not correcting at all.

If you are sure yours is ok, then I would check for vacuum leaks. Reading the forum they seem quite common on older cars.

Sadly I have no better idea and mine is with manual box so no idea what other electronics there might be.

Wait for fixkick to reply, but I though to suggest these as he has been bit more away / responding slowly. Or scroll the forum / docs for diagnosing something with similar issues.

[Zerva5]

Ok so I have a bit of an update. I spent an entire day with my buddy (who has a few spare engines and intakes) and started swapping parts. In total I tried swapping:
MAF
ISC
EGR Main
EGR Modulator
EGR VSV
Plug caps & wires
Distributor Cap
Distributor Rotor

Nothing made a difference. I ended up swapping back to my EGR right before I left to go home but left the rest of his parts on there. On the way home I noticed that the stuttering was gone! However I was having idle issues. The car actually died once at a stop light. I drove it like this for a few days until today when I decided to diagnose and hopefully fix the idle issue. Swapped the ISC again which made no difference and then tried to swap the EGR. Once I pulled the EGR off I saw what was really going on. While putting it on I had managed to let the gasket slip off of the top bolt and it was covering one of the holes. Once I fixed this gasket and tested it again the stuttering was back.

My new theory is that my ECU is bad and is constantly restarting which is then triggering the VSV to cycle closed (allowing the EGR to open and introduce exhaust gas to the intake, making it bog) and closed (closing the EGR and letting the engine recover). I was looking at this the below image and I'm assuming that the VSV is used to vent pressure at light load and corresponds to the bottom left "0 EGR Ratio" part of the graph.


If this is the case then I think the ECU might be the answer. I'm going to open it up and see if there is any obvious corrosion. Otherwise I'm going to replace the injectors but I don't see how that would help.

Car also idles a bit low, when coming to a stop it will sit at 800 for a few seconds but then drop down to 600-650.

So to conclude it's still is annoying and makes me want to bang my head on the steering wheel.

Thanks!

[jwunsch]

If you open the ECU the first thing to do is to check capacitors. Looks like they are quite common problem.

https://fixkick.com/ecu

[Zerva5]

If you open the ECU the first thing to do is to check capacitors. Looks like they are quite common problem.

https://fixkick.com/ecu

Opened it up and capacitors look fine. I can tell thing thing has never been cracked open. I've gone ahead and ordered some replacements for the 2 that go bad most often. The board as a whole looks very clean. Will update if I make any more progress.

[fixkick]

Hello! I've been trying to diagnose this annoying issue on and off for a few months now. The main symptom is at low throttle the engine seems to stumble and recover, stumble then recover, which results in the car jerking forward every time it recovers. I would say it repeats this stumble recover cycle repeats a few times a second.

At first I thought it was EGR related. It passes the stall test however during the live test the EGR valve wasn't moving. I also saw that the idle was very smooth and there was no stumbling. After doing some research I concluded that my sidekick was one of the ones in 1994 where the wheels needed to be spinning for the EGR to engage. I didn't have access to a jack at the time but I tried lightly revving it in neutral while stopped as well as while moving and found that it wouldn't stumble when I wasn't moving but would stumble when I was coasting.

Today I was able to use my buddies jack and did the live test which it passed. Interestingly even with the wheels spinning I wasn't able to make it stumble revving it in neutral. I was also thinking it may have been ECU related and that the VSV was opening and closing and making it stumble. I didn't hear any clicking from the VSV or ISC solenoid so I ruled that out for now.

My buddy is buying a used engine that has a MAF sensor I'm going to throw on and see how it goes. The engine also sounds like it is misfiring a bit at idle. Nothing too bad however.

Things I've checked/done:
VSV: Blowing through it and with 12v
EGR Main: cleaned it top to bottom
EGR Diaphragm: Checked for a clog, there was one, unclogged it, didn't change anything
TPS: Replaced with a used one and calibrated it, no difference
Spark plugs: Replaced
Air Filter: Very clean
MAF: Its clean, didn't check anything else


What I'm planning to do:
Distributor Cap
Distributor Rotor
Plug Wires
Fuel Filter
Check for vacuum leaks
Change timing belt & water pump

I'm not really sure where to go from here, I have an entire used intake I was thinking of doing a deep clean on and swapping in but wonder if you have any other ideas.

Thanks!

stumble,   well  there are lots of causes,  and tests are many to find it.
first off not parked, (auto trans or stick m/t?) how many doors. is this 16v engine. telll what drive line this is first. 4doors is 16v is 4dr.
or only underload, ? only driving? or both? drive and parked.?

1994 , no scan tool works till 1996 usa
so no P03xx codes to find. misfire.
what this is ,
engine bad? cam belt slipped> and ignored
low fuel pressure and FPR bad. fuel pressure all wrong and FPR test fails. see FPR page fixkick.com

spark caused,  or is it fuel related too much or too little.\
lost of 12vdc power via fuse box even loose , IG-coil, , FI and fuses?
bad grounds ? to all that 

the EGR can be just  shut off and make sure EGR main is closed fully and and is easy, just unplug EGR hose at main and golf tEE the hose so it can not suck AIR at hose.
then run with EGR dead, see it still stumbles in 15min test, so simple and easy.  if does stumble now it is not the EGR fault.
spark and fuel wrong, or engine compression bad.

one cause is the spark dies as engine flexes under load, bad grounds at Distrib (dizzy)   the spark just dies dead then comes back under load ends. bad connections at dizzy
I wonce had car like this do that,  I pulled engine hood, off car, and taped a timing light to the wind shield. mag prob to #1 or #4 spark plug , trigger on gun taped (duct) closed
started  car and the strobe flashing perfectly drove around block and only gently turning left ,  spark died. wow, on new Cuttless
the fire wall plug for spark , has  a bent pin at the factory,  nobody could find it for sure not the dealer.
so that is one test to find spark dead.
test 2 is fuel pressure idle keyon not start then at idle in spec,
then fuel pressure under load, not going dead. or blow 30psi.

wot is 36psi and idle is 30 and 6 psi change under full load 16v only, is yours 16v????????
see my graph from my 1996.  16v. G16B 2door.

http://fixkick.com/sensors/tests/FPress-reg1.html

or O2 sensor bad, or exhaust leaks, so unplug the o2 connector now ECU sees 0.45vd for perfect voltage and if no more stumble now,  bingo (o2 bad or exh leak near buy it)

89-95 year take hard work lacking OBD2 ECU. and scan tools cheap. 1996up. usa.

[fixkick]

egr is the first thing to defeat, i can do it in 10min flat or less golf Tee in hand, stalls or surges now? yes, = not EGR , move on forget EGR find the real problem.
sure defeated ECU CEL flash code 51 = EGR dead sure. did you ever look for flash codes (DTC errors at all?)
under hood of car, look up ,. under hood see that suzuki huge sticker label sure , at the bottom does it say california at all???????????????? uses custom EGR it does. if yes.
4 EGRs that year, 2 for 8v and 2 for 16v, cal fed, not to be mixed up. but I defeat it and test the car all ways from sunday.

if put in a $300 rebuilt ECU and still surges how fun is that? and YES 28 year old caps love to dry out that is there spec life span,. electrolytic for sure the huge corner one.
under cab dash temps can hit 250f (in the hot desert ) caps hate that.(lower life.

define the surge better
parked and driving and wot? does car have full power wot????????????? wide open throttle is WOT.
in only one gear.
or at anytime right foot moves, or only when xyz.
FPR loves to fain now, warning, they are at EOL.
so do fuel pumps go weak (the motor commutator is bad segments )and goes weak. like clock work all old cars. BOSCH makes a better pump.
bad grounds spark or fuel
bad spark lots of causes.
fuel pressure does not regulate BAD FPR.
or weak pump.
o2 sensor bad.

:?????