AAAAND that made it worse

cameronl

Member
Been having idle issues for a couple of months with my gli 4g15. Revs will bounce by about 100rpm at idle, itll sit at 1000rpm then suddenly drop to 800 then go back to 1000rpm after accelerating. There is also a rattle from the front of the engine (one bolt holding the ac /p/s assembly to the block IS missing), and a very slight misfire at idle. Mechanic didnt think the rattle was valves or anything internal. There is no CEL. Car is always run on 95

Things i have done to try fix:
New dist cap (forgot to mark before taking of and wasnt put on in correct position. didnt affect anything. engine ran the same)
New dist o ring
New spark plugs
New ignition leads
New Fuel filter
New p/s a/c belt (still need to change alt belt)
New tb
Tried 3 different ISC
Checked TPS voltages (0.9 and 4.8)
Cleaned throttle body and intake (no gap around butterfly valve)
Injector cleaner (wynn's)
Valve cleaner (wynn's)
Tested PCV valve (air goes one way)

None of that worked and issue remains.
Had ignition timing checked and adjusted (was on 25 degrees) Changed to 5 degree as noted in service manual.
Since i had the ignition timing adjusted, the car has no or very sluggish acceleration below 3000rpm. Even a slight hill in 3rd at 60 with foot flat to the floor and ill still lose speed. Other issues remain.

What ive done since adjusting ignition:
Replaced most vacuum hoses (got brake booster and purge solenoid lines left)

Things to try:
Ill be rechecking the tps in the morning to make sure it is still set right.
I do also have a new o2 sensor. is it worth swapping it out?
Test purge solenoid

What else could be causing the issue with the acceleration?
 
Ignition timing 100%. 5* is standard, but if you're running it full time on 95, you can ramp it up a little above stock. More timing will give more torque.
The rattle would likely be from the missing bolt, it might look like theres no play in the compressor/pump, but the engine does make a lot more force than a human can make and it will have gaps and rattle as a result.
TPS would usually set off a CEL when it's set I correctly, but only if its below the 0 marker. If its above this it'll still work but can feel sloppy.
 
Ignition timing 100%. 5* is standard, but if you're running it full time on 95, you can ramp it up a little above stock. More timing will give more torque.
The rattle would likely be from the missing bolt, it might look like theres no play in the compressor/pump, but the engine does make a lot more force than a human can make and it will have gaps and rattle as a result.
TPS would usually set off a CEL when it's set I correctly, but only if its below the 0 marker. If its above this it'll still work but can feel sloppy.
Shouldnt it still run properly when set to factory tho?
Guess ill adjust the dist again
what about the rough idle, it had that before adjusting the dist (this was the main issue i was trying to fix). what else can i try to fix that
 
It should still run well yes. The engines were severely underpowered from factory so I think we all always assume it'll have a big more go than it does. If I were you, move the dizzy about a quarter of the way back to where it was and see how much if any difference it makes.
A rough idle on the 4g15 is usually the tps being a little bit out of reference. Your dizzy idle timing might stabilise that, as that's how modern cars get a smooth idle (running up to 15* advance at idle). Multimeter and the gregorys manual are golden for the tps settings.
 
It should still run well yes. The engines were severely underpowered from factory so I think we all always assume it'll have a big more go than it does. If I were you, move the dizzy about a quarter of the way back to where it was and see how much if any difference it makes.
A rough idle on the 4g15 is usually the tps being a little bit out of reference. Your dizzy idle timing might stabilise that, as that's how modern cars get a smooth idle (running up to 15* advance at idle). Multimeter and the gregorys manual are golden for the tps settings.
Adjusted the dizzy about 4mm from the 25 or so he adjusted it nd def running better. gonna adjust another little bit tomorrow. idle issue remains tho. reckon swap the o2 sensor?
 
It sounds like a vacuum leek, check the vacuum hose that goes to the break booster.
yeah thats the only one i havent changed yet. hopefully that does fix it otherwise smoke test it is. altho swapping the o2 sensor for a new has helped big time. gotta test the isc as well properly as i drop 500 rpm with just the fan on (no a/c)
 
It sounds like a vacuum leek, check the vacuum hose that goes to the break booster.
so i have now replace ALL vacuum lines and rough idle remains so unless its leaking through a gasket. Itll idle while cold at 1200rpm like it should, once warm itll sit on 1000rpm at idle for a while then drop to 800 then a bit later itll drop to 600. once its on 600 itll stay there. turning my fan on full (not a/c) the revs will drop some more but wont go back up like it should when the isc adjusts. i have tried 3 different isc's (cant see ALL 3 of them having issues). when turning the ignition to on (acc) you can her the clicking of the isc (at least i think its the isc). im guessing next step is the smoke test?
 
Advance the timing until it starts to ping and then back it off a few degrees till t stops pinging. For the unsteady idle get some carby cleaner and while the engine is cool and running spray around the inlet listening for where the idle speed steadies.
 
Advance the timing until it starts to ping and then back it off a few degrees till t stops pinging. For the unsteady idle get some carby cleaner and while the engine is cool and running spray around the inlet listening for where the idle speed steadies.
ok so i had the mechanic spray all around the intake, injectors, rocker cover and basically th entire back half of the engine and there was no change in idle speeds and idle still fluctuates. he suggested the MAP sensor (4g15) and car died once it was disconnected. there is still the misfire at idle as well. all spark plugs are clean and do not indicate a rich/lean mixture. gonna adjust the dist some more as see what happenes
 
I would advise you get a multimeter and a Gregory’s and check the values against the recommended values for the TPS MAP and IAT sensors..... I think it should have an IAT. And have you checked your exhaust? If the cat is clogged it can cause all manner of odd running issues depending on how badly it's restricting the flow. Also a gasket leak with the exhaust with screw with the o2 sensor readings? Has the ECU loom been hacked into anywhere? Random shorts screw with how the car will run as well
 
I would advise you get a multimeter and a Gregory’s and check the values against the recommended values for the TPS MAP and IAT sensors..... I think it should have an IAT. And have you checked your exhaust? If the cat is clogged it can cause all manner of odd running issues depending on how badly it's restricting the flow. Also a gasket leak with the exhaust with screw with the o2 sensor readings? Has the ECU loom been hacked into anywhere? Random shorts screw with how the car will run as well
already checked the tps which is reading .9v closed and 4.95v open which is within specs according to the Gregory's. havent checked the MAP sensor but car does die when it is unplugged and the IACV/ISC (i think thats what you mean by IAT) clicks properly when turning the ignition on. also the revs jump to 2000rpm when you unplug it indicating it is also working correctly. I took the distributor of yesterday and noticed there was oil around the back seal altho the o ring is still good. i think oil is leaking in through the dist shaft so gonna grab some contact cleaner and give the dist a really good spray. after doing a wipe down yesterdaqy the engine did sound and behave better
 
IAT is Intake Air Temperature (it's built into the MAF sensor housing normally but 4g15 doesn't use this and I really don't remember if it has one or is maybe built into MAP sensor)
 
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