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Old 08-29-2017, 09:25 PM
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Join Date: Oct 2013
Posts: 16
1997 S420 - rough/smelly start when outside temp is HOT

I have a 1997 S420 - I've noticed an issue with the idle at startup - particularly when it is hot outside (over 90). The car starts really rough (feels like dropping a cylinder) then as it "warms up" - it smoothes out, it's always had a bit of a miss in the idle (like, REALLY minor - I'm the only one that can notice it) and when it starts rough it smells really gassy (which could just be attributed to too much unburnt fuel passing out the tailpipe - since it clearly is missing)

I've checked as well as I can the vacuum lines
and replaced the temp sending unit (changed it unrelated to this issue - but I've noticed this problem before changing the temp sending unit.)
I have a new purge valve on order (since I would wager the one in the car is original)

Anything else I should look into?

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Old 08-29-2017, 09:34 PM
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Join Date: Oct 2004
Posts: 3,227
Leaking fuel pressure regulator? Pull the hose off and check for gas.
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
4 ignition advance
PCS TCM2000 running 722.6 trans, 600W PWM fan, water injection
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff
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Old 09-20-2017, 02:58 PM
Registered User
Join Date: Oct 2013
Posts: 16
Not Fuel regulator

Wasn't the regulator, but I replaced it anyway. I did find a couple small leaks in some vacuum lines (replaced them) Idles REALLY smooth now... BUT

I get a p0410 code...

so -

Does anyone know how to pull the valve without taking the fron of the engine apart? the screws/bolts are on the underside of the valve and I don't know how to reach them.

Does anyone know the routing of the secondary air system? Does it dump directly into the exhaust pipe, or does it go through the head - if through the head I think I'm lost... I don't want to pull the heads...


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