Help! My son’s 1988 MK2 Golf GTI recently began a most curious random rough idle, occasionally to a stall, especially when turning abruptly, or when initiating a stop with the clutch depressed, and now always when turning at low speeds in combination with brake application. This only occurs when the engine is warm. The braking clue first led me to investigate the brake vacuum booster as they will cause that symptom when they fail internally, but if they fail, the sudden low , rough idle symptom is repeatable. This is not the case. Sitting in the driveway I can depress the brakes firmly with no change in engine rpm. Idle stays steady and normal. So I checked carefully for vacuum leaks, found none. Checked all the fuel system sensors and idle speed regulators, all are in order. New battery, good output from the alternator, ignition timing strobe is steady and bright. All the air intake rubber is like new. The in-tank fuel transfer pump works. The high pressure external fuel pump works. I found this same issue searching here but no resolution to this unusual “only when moving” problem was posted.
OK so I have been able to make some progress. After replacing the distributor cap and rotor, the problem persists, but engine rpm dips to only 500 or so, and the engine does not die anymore ni a turn or when braking. Progress, but not a complete solution. The fuel pressure regulator is barely seeping, so little that a leak is not evident but if one wipes a finger underneath the regulator, a trace dampness of fuel is present. So that is next on he investigation list.
@LaVoce there’s nothing to investigate. It needs to be replaced. It should be dry as a bone.
Hi DB4690, thanks for the comment. There are two O rings that seal the pressure regulator to the fuel manifold. At $18 as compared to $400 for the regulator, I will replace those first and see what that does to my trace seepage. Tonight my son told me after filling the fuel tank on the way home, all symptoms are gone. Idles rock steady when stopped and under all dynamic conditions including turns. Hmmm. Partially blocked vent line? Obstruction in the fuel tank? When I drove the car this past weekend, it was exhibiting these strange symptoms, and the fuel gauge indicated the tank was about 3/4 full. As a side note, the car was also making a groaning or creaking noise when starting off from a stop, or occasionally when shifting from 1st to 2nd gear. It was always difficult to determine the location of the noise- sometimes it seeemed as if it came from the front of the car, sometimes the back, sometimes the left, sometimes the right, we could not tell exactly where it was coming from. It’s been doing this for some time, even preceeding the strange idle problem. I had thought this was a bushing, or a motor mount, or suspension related, but now I wonder if it is a fuel pump cavitating, or air in the system. The thing is, it is never directly related to the idle problem (e.g., it’s never the haunted house creek/ groan shortly followed by an idle incident, it’s just random)
@LaVoce you are getting RIPPED OFF. Whoever’s selling you a $400 fuel pressure regulator needs to join Bernie Madoff in the big house.
Enlighten me please! Everywhere I look I see pricing ranging from $386 to $430.
@LaVoce parts and labor?
Chilton labor time is 1.3hrs, by the way.
Post us a picture of the part, please.
Which one do you have?
It’s the first one, the Bosch Part Number W0133-1599941differential pressure regulator that attaches directly to the fuel distributor. I should have been clear about that nomenclature. No labor cost, I work for beer! By the way, the “full tank of fuel makes the symptoms disappear” theory was debunked yesterday. Arrgh. I hate random intermittent problems. Back down into the troubleshooting mine.
OK so here’s what happened. The engine near-stall condition progressed to the point where sitting in the driveway, all I had to do was blip the throttle to above 2,000 rpm or so and upon return to idle, it nearly died but recovered. I was able to consistently repeat this. So as I traced the knock sensor harness back towards the sensor, I found it was unplugged. Plugging it in solved the problem completely. Smooth idle at all times now.