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Book page: Throttle Air Bypass ISC text with idle RPM vs coolant…

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Scanned page from a Warm Idle Strategy #9 reference, section 9.3 "Throttle Air Bypass (ISC)," describing how idle air bypass opens after 1-4 minutes to add about 80 rpm and how coolant or intake air above 105°C (225°F) triggers further idle-speed increases only in Neutral or Park. Figure 9-2 graphs RPM added to base idle speed against engine coolant temperature, falling from 400 rpm at 0°F to near zero around 175°F before rising again past 200°F.

AI caption July 2011 · Photo 159 of 221

9.3 Throttle Air Bypass (ISO) Warm Idle Thmllle Alt Bypass Increases gradually alter 1 minule, Thls maintains Idle rpm even with sperkllmlng retard Alter 4 minules. the thralllealt bypass opens slightly to ins oreese ehglns speed abdui so rpm. ll! this rpm Increase is limited unless lheA/Tls In Neutral or Park to prevent aulamar Ic-Itensmtssion cteep. Wenn Idle can xurn lntu hm idle, and the oanlrol module in- cludes a slrategy lo leduce ovemeallng: - ll coolanl nses aoove 10500 (225% the obnltel module slgnals |he Thlonle Alt Bypass to increase Walm Idle engine speed aboul 100 rpm Il dbos this only Iwr IS in Neuuel a! Park - II the inlake-alrlampamlms Is above 105!) l225Flt lhe conuol module slgnals Ihe Tntellle Alt Bypass Io ihetease Wetnt Idle 809an speed ahuul 25 rpm. ll does this only ll NT is In Neuttal or Park Idle RPM lncteases allow coolanl (empelalules and am dunnd ovemeat commons RPM 500 added to base 20 Idle speed we 0' 25' 50' 75 ml? 50 200 250- Engne coolant lempeiatute In deg-es Famenrvlll E732: Plum ngh Englne cadlanl (amperalwes (ECTiaDm/e 225$) WIII cause controlmrxlulo to Increase Idle Ypm about too tpm WARM IDLE~STRA TEGY # 9

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