Just plug the line going to the engine. You don't want to plug the tank side and have excess pressure cause another problem in the purge system. Once you've confirmed it has a problem, I'd just go ahead and replace it. It's not terribly expensive and you don't have to worry about it anytime in the near future. Otherwise you could end up futzing with it off and on until you do replace it.


Latief, yes a leaking valve can cause mixture problems, especially when stuck wide open. You may have other problems but the above advice applies to you as well.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff